Quantum dot devices with multiple layers of gate metal

ABSTRACT

Disclosed herein are quantum dot devices with multiple layers of gate metal, as well as related computing devices and methods. For example, in some embodiments, a quantum dot device may include: a quantum well stack; an insulating material above the quantum well stack, wherein the insulating material includes a trench; and a gate on the insulating material and extending into the trench, wherein the gate includes a first gate metal in the trench and a second gate metal above the first gate metal.

BACKGROUND

Quantum computing refers to the field of research related to computation systems that use quantum mechanical phenomena to manipulate data. These quantum mechanical phenomena, such as superposition (in which a quantum variable can simultaneously exist in multiple different states) and entanglement (in which multiple quantum variables have related states irrespective of the distance between them in space or time), do not have analogs in the world of classical computing, and thus cannot be implemented with classical computing devices.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be readily understood by the following detailed description in conjunction with the accompanying drawings. To facilitate this description, like reference numerals designate like structural elements. Embodiments are illustrated by way of example, not by way of limitation, in the figures of the accompanying drawings.

FIGS. 1-4 are cross-sectional views of an example quantum dot device, in accordance with various embodiments.

FIGS. 5-44 illustrate various example stages in the manufacture of the quantum dot device of FIGS. 1-4 , in accordance with various embodiments.

FIGS. 45-47 are cross-sectional views of another example quantum dot device, in accordance with various embodiments.

FIG. 48 is a cross-sectional view of another example quantum dot device, in accordance with various embodiments.

FIG. 49 is a cross-sectional view of an alternative example stage in the manufacture of the quantum dot device of FIG. 48 , in accordance with various embodiments.

FIGS. 50-52 are cross-sectional views of various examples of quantum well stacks that may be used in a quantum dot device, in accordance with various embodiments.

FIGS. 53-54 illustrate detail views of various embodiments of a doped region in a quantum dot device, in accordance with various embodiments.

FIG. 55A illustrates an embodiment of a quantum dot device having multiple trenches arranged in a two-dimensional array, in accordance with various embodiments.

FIG. 55B illustrates an embodiment of a quantum dot device having multiple groups of gates in a single trench on a quantum well stack, in accordance with various embodiments.

FIGS. 56-59 illustrate various alternative stages in the manufacture of a quantum dot device, in accordance with various embodiments.

FIGS. 60 and 61 are cross-sectional views of other examples of quantum dot devices, in accordance with various embodiments.

FIG. 62 is a cross-sectional view of a quantum dot device with multiple interconnect layers, in accordance with various embodiments.

FIG. 63 is a cross-sectional view of a quantum dot device package, in accordance with various embodiments.

FIGS. 64A and 64B are top views of a wafer and dies that may include any of the quantum dot devices disclosed herein.

FIG. 65 is a cross-sectional view of a device assembly that may include any of the quantum dot devices disclosed herein.

FIG. 66 is a flow diagram of an illustrative method of operating a quantum dot device, in accordance with various embodiments.

FIG. 67 is a block diagram of an example quantum computing device that may include any of the quantum dot devices disclosed herein, in accordance with various embodiments.

DETAILED DESCRIPTION

Disclosed herein are quantum dot devices with multiple layers of gate metal, as well as related computing devices and methods. For example, in some embodiments, a quantum dot device may include: a quantum well stack; an insulating material above the quantum well stack, wherein the insulating material includes a trench; and a gate on the insulating material and extending into the trench, wherein the gate includes a first gate metal in the trench and a second gate metal above the first gate metal.

The quantum dot devices disclosed herein may enable the formation of quantum dots to serve as quantum bits (“qubits”) in a quantum computing device, as well as the control of these quantum dots to perform quantum logic operations. Unlike previous approaches to quantum dot formation and manipulation, various embodiments of the quantum dot devices disclosed herein provide strong spatial localization of the quantum dots (and therefore good control over quantum dot interactions and manipulation), good scalability in the number of quantum dots included in the device, and/or design flexibility in making electrical connections to the quantum dot devices to integrate the quantum dot devices in larger computing devices.

In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown, by way of illustration, embodiments that may be practiced. It is to be understood that other embodiments may be utilized, and structural or logical changes may be made, without departing from the scope of the present disclosure. Therefore, the following detailed description is not to be taken in a limiting sense.

Various operations may be described as multiple discrete actions or operations in turn in a manner that is most helpful in understanding the claimed subject matter. However, the order of description should not be construed as to imply that these operations are necessarily order dependent. In particular, these operations may not be performed in the order of presentation. Operations described may be performed in a different order from the described embodiment. Various additional operations may be performed, and/or described operations may be omitted in additional embodiments.

For the purposes of the present disclosure, the phrase “A and/or B” means (A), (B), or (A and B). For the purposes of the present disclosure, the phrase “A, B, and/or C” means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C). The term “between,” when used with reference to measurement ranges, is inclusive of the ends of the measurement ranges. As used herein, the notation “A/B/C” means (A), (B), and/or (C).

The description uses the phrases “in an embodiment” or “in embodiments,” which may each refer to one or more of the same or different embodiments. Furthermore, the terms “comprising,” “including,” “having,” and the like, as used with respect to embodiments of the present disclosure, are synonymous. The disclosure may use perspective-based descriptions such as “above,” “below,” “top,” “bottom,” and “side”; such descriptions are used to facilitate the discussion and are not intended to restrict the application of disclosed embodiments. The accompanying drawings are not necessarily drawn to scale. As used herein, a “high-k dielectric” refers to a material having a higher dielectric constant than silicon oxide. As used herein, a “magnet line” refers to a magnetic field-generating structure to influence (e.g., change, reset, scramble, or set) the spin states of quantum dots. One example of a magnet line, as discussed herein, is a conductive pathway that is proximate to an area of quantum dot formation and selectively conductive of a current pulse that generates a magnetic field to influence a spin state of a quantum dot in the area.

FIGS. 1-4 are cross-sectional views of a quantum dot device 100, in accordance with various embodiments. In particular, FIG. 2 illustrates the quantum dot device 100 taken along the section A-A of FIG. 1 (while FIG. 1 illustrates the quantum dot device 100 taken along the section C-C of FIG. 2 ), FIG. 3 illustrates the quantum dot device 100 taken along the section D-D of FIG. 2 (while FIG. 2 illustrates the quantum dot device 100 taken along the section A-A of FIG. 3 ), and FIG. 4 illustrates the quantum dot device 100 taken along the section B-B of FIG. 1 with a number of components not shown to more readily illustrate how the gates 106/108 and the magnet line 121 may be patterned (while FIG. 1 illustrates a quantum dot device 100 taken along the section E-E of FIG. 4 ). Although FIG. 1 indicates that the cross-section illustrated in FIG. 2 is taken through the trench 104-1, an analogous cross-section taken through the trench 104-2 may be identical, and thus the discussion of FIG. 2 refers generally to the “trench 104.”

The quantum dot device 100 may include a quantum well stack 146 disposed on a base 102. An insulating material 128 may be disposed above the quantum well stack 146, and multiple trenches 104 in the insulating material 128 may extend toward the quantum well stack 146. In the embodiment illustrated in FIGS. 1-4 , a gate dielectric 114 may be disposed between the quantum well stack 146 and the insulating material 128 so as to provide the “bottom” of the trenches 104. A number of examples of quantum well stacks 146 are discussed below with reference to FIGS. 50-52 .

Although only two trenches, 104-1 and 104-2, are shown in FIGS. 1-4 , this is simply for ease of illustration, and more than two trenches 104 may be included in the quantum dot device 100. In some embodiments, the total number of trenches 104 included in the quantum dot device 100 is an even number, with the trenches 104 organized into pairs including one active trench 104 and one read trench 104, as discussed in detail below. When the quantum dot device 100 includes more than two trenches 104, the trenches 104 may be arranged in pairs in a line (e.g., 2N trenches total may be arranged in a 1×2N line, or a 2×N line) or in pairs in a larger array (e.g., 2N trenches total may be arranged as a 4×N/2 array, a 6×N/3 array, etc.). For example, FIG. 55A illustrates a quantum dot device 100 including an example two-dimensional array of trenches 104. As illustrated in FIGS. 1 and 3 , in some embodiments, multiple trenches 104 may be oriented in parallel. The discussion herein will largely focus on a single pair of trenches 104 for ease of illustration, but all the teachings of the present disclosure apply to quantum dot devices 100 with more trenches 104. Further, the use of the term “trench” should not be interpreted to require that the insulating material 128 is deposited first and then a portion of that insulating material 128 is excavated to form the trench 104 prior to depositing material in the trench 104; as discussed further below, the insulating material 128 may be deposited before or after deposition of the material that will ultimately be disposed in the trench 104.

The quantum well stack 146 may include a quantum well layer (not shown in FIGS. 1-4 , but discussed below with reference to the quantum well layer 152 of FIGS. 50-52 ). The quantum well layer included in the quantum well stack 146 may be arranged normal to the z-direction, and may provide a layer in which a two-dimensional electron gas (2DEG) may form to enable the generation of a quantum dot during operation of the quantum dot device 100, as discussed in further detail below. The quantum well layer itself may provide a geometric constraint on the z-location of quantum dots in the quantum well stack 146. To control the x- and y-location of quantum dots in the quantum well stack 146, voltages may be applied to gates disposed at least partially in the trenches 104 above the quantum well stack 146 to adjust the energy profile along the trenches 104 in the x- and y-direction and thereby constrain the x- and y-location of quantum dots within quantum wells (discussed in detail below with reference to the gates 106/108). The dimensions of the trenches 104 may take any suitable values. For example, in some embodiments, the trenches 104 may each have a width 162 between 5 nanometers and 30 nanometers. In some embodiments, the trenches 104 may each have a depth 164 between 40 nanometers and 400 nanometers (e.g., between 70 nanometers and 350 nanometers, or equal to 300 nanometers). The insulating material 128 may be a dielectric material (e.g., an interlayer dielectric), such as silicon oxide. In some embodiments, the insulating material 128 may be a chemical vapor deposition (CVD) or flowable CVD oxide. In some embodiments, the trenches 104 may be spaced apart by a distance 160 between 50 nanometers and 500 nanometers.

Multiple gates may be disposed at least partially in each of the trenches 104. In the embodiment illustrated in FIG. 2 , three gates 106 and two gates 108 are shown as distributed at least partially in a single trench 104. This particular number of gates is simply illustrative, and any suitable number of gates may be used. Additionally, as discussed below with reference to FIG. 55B, multiple groups of gates (like the gates illustrated in FIG. 2 ) may be disposed at least partially in the trench 104.

As shown in FIG. 2 , the gate 108-1 may be disposed between the gates 106-1 and 106-2, and the gate 108-2 may be disposed between the gates 106-2 and 106-3. Each of the gates 106/108 may include a gate dielectric 114; in the embodiment illustrated in FIG. 2 , the gate dielectric 114 for all of the gates 106/108 is provided by a common layer of gate dielectric material disposed between the quantum well stack 146 and the insulating material 128. In other embodiments, the gate dielectric 114 for each of the gates 106/108 may be provided by separate portions of gate dielectric 114 (e.g., as discussed below with reference to FIGS. 56-59 ). In some embodiments, the gate dielectric 114 may be a multilayer gate dielectric (e.g., with multiple materials used to improve the interface between the trench 104 and the corresponding gate metal). The gate dielectric 114 may be, for example, silicon oxide, aluminum oxide, or a high-k dielectric, such as hafnium oxide. More generally, the gate dielectric 114 may include elements such as hafnium, silicon, oxygen, titanium, tantalum, lanthanum, aluminum, zirconium, barium, strontium, yttrium, lead, scandium, niobium, and zinc. Examples of materials that may be used in the gate dielectric 114 may include, but are not limited to, hafnium oxide, hafnium silicon oxide, lanthanum oxide, lanthanum aluminum oxide, zirconium oxide, zirconium silicon oxide, tantalum oxide, titanium oxide, barium strontium titanium oxide, barium titanium oxide, strontium titanium oxide, yttrium oxide, aluminum oxide, tantalum oxide, tantalum silicon oxide, lead scandium tantalum oxide, and lead zinc niobate. In some embodiments, an annealing process may be carried out on the gate dielectric 114 to improve the quality of the gate dielectric 114.

Each of the gates 106 may include a gate metal 110 (including multiple layers of gate metal) and a hardmask 116. In particular, a first gate metal layer 110A may be disposed in the trench 104, and a second gate metal layer 110B may be disposed above the gate metal 110-1 and above the insulating material 128, as shown. The hardmask 116 may be formed of silicon nitride, silicon carbide, or another suitable material. The gate metal 110 may be disposed between the hardmask 116 and the gate dielectric 114, and the gate dielectric 114 may be disposed between the gate metal 110 and the quantum well stack 146. As shown in FIG. 1 , in some embodiments, the gate metal 110 of a gate 106 may extend over the insulating material 128 and into a trench 104 in the insulating material 128. Only one portion of the hardmask 116 is labeled in FIG. 2 for ease of illustration.

In some embodiments, the gate metal 110 may be a superconductor, such as aluminum, titanium nitride, or niobium titanium nitride; any of these materials may be included in the first gate metal layer 110A and/or the second gate metal layer 110B. In some embodiments, the first gate metal layer 110A may have a different material composition than the second gate metal layer 110B. For example, the first gate metal layer 110A (the second gate metal layer 110B) may be titanium nitride, while the second gate metal layer 110B (the first gate metal layer 110A) may be a material different from titanium nitride. In some embodiments, the first gate metal layer 110A and the second gate metal layer 110B may have a same material composition, but may have a different microstructure. These different microstructures may arise, for example, by different deposition and/or patterning techniques used to form the first gate metal layer 110A and the second gate metal layer 110B, as discussed further below. For example, in some embodiments, the first gate metal layer 110A may have a microstructure including columnar grains (e.g., when the first gate metal layer 110A is initially blanket-deposited and then etched as part of a subtractive patterning process, as discussed further below), while the second gate metal layer 110B may not exhibit a columnar grain structure. In some embodiments, a seam delineating the interface between the top surface of the first gate metal layer 110A and the bottom surface of the second gate metal layer 110B may be present in the quantum dot device 100.

In some embodiments, the hardmask 116 may not be present in the quantum dot device 100 (e.g., a hardmask like the hardmask 116 may be removed during processing, as discussed below). The sides of the gate metal 110 may be substantially parallel, as shown in FIG. 2 , and insulating spacers 134 may be disposed on the sides of the gate metal 110 and the hardmask 116 along the longitudinal axis of the trench 104. As illustrated in FIG. 2 , the spacers 134 may be thicker closer to the quantum well stack 146 and thinner farther away from the quantum well stack 146. In some embodiments, the spacers 134 may have a convex shape. The spacers 134 may be formed of any suitable material, such as a carbon-doped oxide, silicon nitride, silicon oxide, or other carbides or nitrides (e.g., silicon carbide, silicon nitride doped with carbon, and silicon oxynitride). As illustrated in FIG. 2 , no spacer material may be disposed between the gate metal 110 and the sidewalls of the trench 104 in the y-direction.

Each of the gates 108 may include a gate metal 112 and a hardmask 118. The hardmask 118 may be formed of silicon nitride, silicon carbide, or another suitable material. The gate metal 112 may be disposed between the hardmask 118 and the gate dielectric 114, and the gate dielectric 114 may be disposed between the gate metal 112 and the quantum well stack 146. As shown in FIG. 3 , in some embodiments, the gate metal 112 of a gate 108 may extend over the insulating material 128 and into a trench 104 in the insulating material 128. In the embodiment illustrated in FIG. 2 , the hardmask 118 may extend over the hardmask 116 (and over the gate metal 110 of the gates 106), while in other embodiments, the hardmask 118 may not extend over the gate metal 110. In the embodiment of FIGS. 1-3 , the gate metal 112 of the gates 108 may be provided by a single continuous layer of material (and may not, for example, include multiple different layers of gate metal, as was discussed above with reference to the gate metal 110 of the gates 106). In other embodiments, however, the gate metal 112 of the gates 108 may include multiple layers of gate metal; a particular example of such an embodiment is discussed below with reference to FIG. 61 . In some embodiments, the gate metal 112 may be a different metal from the first gate metal layer 110A and/or the second gate metal layer 110B; in other embodiments, the gate metal 112 and the first gate metal layer 110A and/or the second gate metal layer 110B may have the same material composition. In some embodiments, the gate metal 112 may be a superconductor, such as aluminum, titanium nitride, or niobium titanium nitride. In some embodiments, the hardmask 118 may not be present in the quantum dot device 100 (e.g., a hardmask like the hardmask 118 may be removed during processing, as discussed below).

The gate 108-1 may extend between the proximate spacers 134 on the sides of the gate 106-1 and the gate 106-2 along the longitudinal axis of the trench 104, as shown in FIG. 2 . In some embodiments, the gate metal 112 of the gate 108-1 may extend between the spacers 134 on the sides of the gate 106-1 and the gate 106-2 along the longitudinal axis of the trench 104. Thus, the gate metal 112 of the gate 108-1 may have a shape that is substantially complementary to the shape of the spacers 134, as shown. Similarly, the gate 108-2 may extend between the proximate spacers 134 on the sides of the gate 106-2 and the gate 106-3 along the longitudinal axis of the trench 104. In some embodiments in which the gate dielectric 114 is not a layer shared commonly between the gates 108 and 106, but instead is separately deposited in the trench 104 between the spacers 134 (e.g., as discussed below with reference to FIGS. 56-59 ), the gate dielectric 114 may extend at least partially up the sides of the spacers 134 (and up the proximate sidewalls of the trench 104), and the gate metal 112 may extend between the portions of gate dielectric 114 on the spacers 134 (and the proximate sidewalls of the trench 104). As illustrated in FIG. 3 , in some embodiments, no spacer material may be disposed between the gate metal 112 and the sidewalls of the trench 104 in the y-direction; in other embodiments (e.g., as discussed below with reference to FIGS. 48 and 49 ), spacers 134 may also be disposed between the gate metal 112 and the sidewalls of the trench 104 in the y-direction.

The dimensions of the gates 106/108 may take any suitable values. For example, in some embodiments, the z-height 166 of the gate metal 110 in the trench 104 may be between 225 nanometers and 375 nanometers (e.g., approximately 300 nanometers); the z-height 175 of the gate metal 112 may be in the same range. This z-height 166 of the gate metal 110 in the trench 104 may represent the sum of the z-height of the first gate metal layer 110A (e.g., between 40 nanometers and 300 nanometers) and the thickness of the second gate metal layer 110B (e.g., between 25 nanometers and 75 nanometers, or approximately 50 nanometers). In embodiments like the ones illustrated in FIGS. 1-3 , the z-height 175 of the gate metal 112 may be greater than the z-height 166 of the gate metal 110. In some embodiments, the length 168 of the gate metal 110 (i.e., in the x-direction) may be between 20 nanometers and 40 nanometers (e.g., 30 nanometers). Although all of the gates 106 are illustrated in the accompanying drawings as having the same length 168 of the gate metal 110, in some embodiments, the “outermost” gates 106 (e.g., the gates 106-1 and 106-3 of the embodiment illustrated in FIG. 2 ) may have a greater length 168 than the “inner” gates 106 (e.g., the gate 106-2 in the embodiment illustrated in FIG. 2 ). Such longer “outside” gates 106 may provide spatial separation between the doped regions 140 and the areas under the gates 108 and the inner gates 106 in which quantum dots 142 may form, and thus may reduce the perturbations to the potential energy landscape under the gates 108 and the inner gates 106 caused by the doped regions 140.

In some embodiments, the distance 170 between adjacent ones of the gates 106 (e.g., as measured from the gate metal 110 of one gate 106 to the gate metal 110 of an adjacent gate 106 in the x-direction, as illustrated in FIG. 2 ) may be between 40 nanometers and 60 nanometers (e.g., 50 nanometers). In some embodiments, the thickness 172 of the spacers 134 may be between 1 nanometer and 10 nanometers (e.g., between 3 nanometers and 5 nanometers, between 4 nanometers and 6 nanometers, or between 4 nanometers and 7 nanometers). The length of the gate metal 112 (i.e., in the x-direction) may depend on the dimensions of the gates 106 and the spacers 134, as illustrated in FIG. 2 . As indicated in FIGS. 1 and 3 , the gates 106/108 in one trench 104 may extend over the insulating material 128 between that trench 104 and an adjacent trench 104, but may be isolated from their counterpart gates by the intervening insulating material 130 and spacers 134.

As shown in FIG. 2 , the gates 106 and 108 may be alternatingly arranged in the x-direction. During operation of the quantum dot device 100, voltages may be applied to the gates 106/108 to adjust the potential energy in the quantum well stack 146 to create quantum wells of varying depths in which quantum dots 142 may form. Only one quantum dot 142 is labeled with a reference numeral in FIGS. 2 and 4 for ease of illustration, but five are indicated as dotted circles below each trench 104. The location of the quantum dots 142 in FIGS. 2 and 4 is not intended to indicate a particular geometric positioning of the quantum dots 142. The spacers 134 (and the insulating material 128) may themselves provide “passive” barriers between quantum dots under the gates 106/108 in the quantum well stack 146, and the voltages applied to different ones of the gates 106/108 may adjust the potential energy under the gates 106/108 in the quantum well stack 146; decreasing the potential energy under a gate 106/108 may enable the formation of a quantum dot under that gate 106/108, while increasing the potential energy under a gate 106/108 may form a quantum barrier under that gate 106/108.

The quantum well stack 146 may include doped regions 140 that may serve as a reservoir of charge carriers for the quantum dot device 100. For example, an n-type doped region 140 may supply electrons for electron-type quantum dots 142, and a p-type doped region 140 may supply holes for hole-type quantum dots 142. In some embodiments, an interface material 141 may be disposed at a surface of a doped region 140, as shown. The interface material 141 may facilitate electrical coupling between a conductive contact (e.g., a conductive via 136, as discussed below) and the doped region 140. The interface material 141 may be any suitable metal-semiconductor ohmic contact material; for example, in embodiments in which the doped region 140 includes silicon, the interface material 141 may include nickel silicide, aluminum silicide, titanium silicide, molybdenum silicide, cobalt silicide, tungsten silicide, or platinum silicide (e.g., as discussed below with reference to FIGS. 33-34 ). In some embodiments, the interface material 141 may be a non-silicide compound, such as titanium nitride. In some embodiments, the interface material 141 may be a metal (e.g., aluminum, tungsten, or indium).

The quantum dot devices 100 disclosed herein may be used to form electron-type or hole-type quantum dots 142. Note that the polarity of the voltages applied to the gates 106/108 to form quantum wells/barriers depends on the charge carriers used in the quantum dot device 100. In embodiments in which the charge carriers are electrons (and thus the quantum dots 142 are electron-type quantum dots), amply negative voltages applied to a gate 106/108 may increase the potential barrier under the gate 106/108, and amply positive voltages applied to a gate 106/108 may decrease the potential barrier under the gate 106/108 (thereby forming a potential well in which an electron-type quantum dot 142 may form). In embodiments in which the charge carriers are holes (and thus the quantum dots 142 are hole-type quantum dots), amply positive voltages applied to a gate 106/108 may increase the potential barrier under the gate 106/108, and amply negative voltages applied to a gate 106 and 108 may decrease the potential barrier under the gate 106/108 (thereby forming a potential well in which a hole-type quantum dot 142 may form). The quantum dot devices 100 disclosed herein may be used to form electron-type or hole-type quantum dots.

Voltages may be applied to each of the gates 106 and 108 separately to adjust the potential energy in the quantum well stack 146 under the gates 106 and 108, and thereby control the formation of quantum dots 142 under each of the gates 106 and 108. Additionally, the relative potential energy profiles under different ones of the gates 106 and 108 allow the quantum dot device 100 to tune the potential interaction between quantum dots 142 under adjacent gates. For example, if two adjacent quantum dots 142 (e.g., one quantum dot 142 under a gate 106 and another quantum dot 142 under an adjacent gate 108) are separated by only a short potential barrier, the two quantum dots 142 may interact more strongly than if they were separated by a taller potential barrier. Since the depth of the potential wells/height of the potential barriers under each gate 106/108 may be adjusted by adjusting the voltages on the respective gates 106/108, the differences in potential between adjacent gates 106/108 may be adjusted, and thus the interaction tuned.

In some applications, the gates 108 may be used as plunger gates to enable the formation of quantum dots 142 under the gates 108, while the gates 106 may be used as barrier gates to adjust the potential barrier between quantum dots 142 formed under adjacent gates 108. In other applications, the gates 108 may be used as barrier gates, while the gates 106 are used as plunger gates. In other applications, quantum dots 142 may be formed under all of the gates 106 and 108, or under any desired subset of the gates 106 and 108.

Conductive vias and lines may make contact with the gates 106/108, and to the doped regions 140, to enable electrical connection to the gates 106/108 and the doped regions 140 to be made in desired locations. As shown in FIGS. 1-4 , the gates 106 may extend both “vertically” and “horizontally” away from the quantum well stack 146, and conductive vias 120 may contact the gates 106 (and are drawn in dashed lines in FIG. 2 to indicate their location behind the plane of the drawing). The conductive vias 120 may extend through the hardmask 116 and the hardmask 118 to contact the gate metal 110 of the gates 106. The gates 108 may similarly extend away from the quantum well stack 146, and conductive vias 122 may contact the gates 108 (also drawn in dashed lines in FIG. 2 to indicate their location behind the plane of the drawing). The conductive vias 122 may extend through the hardmask 118 to contact the gate metal 112 of the gates 108. Conductive vias 136 may contact the interface material 141 and may thereby make electrical contact with the doped regions 140. The quantum dot device 100 may include further conductive vias and/or lines (not shown) to make electrical contact to the gates 106/108 and/or the doped regions 140, as desired. The conductive vias and lines included in a quantum dot device 100 may include any suitable materials, such as copper, tungsten (deposited, e.g., by CVD), or a superconductor (e.g., aluminum, tin, titanium nitride, niobium titanium nitride, tantalum, niobium, or other niobium compounds such as niobium tin and niobium germanium).

During operation, a bias voltage may be applied to the doped regions 140 (e.g., via the conductive vias 136 and the interface material 141) to cause current to flow through the doped regions 140 and through a quantum well layer of the quantum well stack 146 (discussed in further detail below with reference to FIGS. 50-52 ). When the doped regions 140 are doped with an n-type material, this voltage may be positive; when the doped regions 140 are doped with a p-type material, this voltage may be negative. The magnitude of this bias voltage may take any suitable value (e.g., between 0.25 volts and 2 volts).

In some embodiments, the quantum dot device 100 may include one or more magnet lines 121. For example, a single magnet line 121 is illustrated in FIGS. 1-4 , proximate to the trench 104-1. The magnet line 121 may be formed of a conductive material, and may be used to conduct current pulses that generate magnetic fields to influence the spin states of one or more of the quantum dots 142 that may form in the quantum well stack 146. In some embodiments, the magnet line 121 may conduct a pulse to reset (or “scramble”) nuclear and/or quantum dot spins. In some embodiments, the magnet line 121 may conduct a pulse to initialize an electron in a quantum dot in a particular spin state. In some embodiments, the magnet line 121 may conduct current to provide a continuous, oscillating magnetic field to which the spin of a qubit may couple. The magnet line 121 may provide any suitable combination of these embodiments, or any other appropriate functionality.

In some embodiments, the magnet line 121 may be formed of copper. In some embodiments, the magnet line 121 may be formed of a superconductor, such as aluminum. The magnet line 121 illustrated in FIGS. 1-4 is non-coplanar with the trenches 104, and is also non-coplanar with the gates 106/108. In some embodiments, the magnet line 121 may be spaced apart from the gates 106/108 by a distance 167. The distance 167 may take any suitable value (e.g., based on the desired strength of magnetic field interaction with particular quantum dots 142); in some embodiments, the distance 167 may be between 25 nanometers and 1 micron (e.g., between 50 nanometers and 200 nanometers).

In some embodiments, the magnet line 121 may be formed of a magnetic material. For example, a magnetic material (such as cobalt) may be deposited in a trench in the insulating material 130 to provide a permanent magnetic field in the quantum dot device 100.

The magnet line 121 may have any suitable dimensions. For example, the magnet line 121 may have a thickness 169 between 25 nanometers and 100 nanometers. The magnet line 121 may have a width 171 between 25 nanometers and 100 nanometers. In some embodiments, the width 171 and thickness 169 of a magnet line 121 may be equal to the width and thickness, respectively, of other conductive lines in the quantum dot device 100 (not shown) used to provide electrical interconnects, as known in the art. The magnet line 121 may have a length 173 that may depend on the number and dimensions of the gates 106/108 that are to form quantum dots 142 with which the magnet line 121 is to interact. The magnet line 121 illustrated in FIGS. 1-4 (and the magnet lines 121 illustrated in FIGS. 45-47 below) are substantially linear, but this need not be the case; the magnet lines 121 disclosed herein may take any suitable shape. Conductive vias 123 may contact the magnet line 121.

The conductive vias 120, 122, 136, and 123 may be electrically isolated from each other by an insulating material 130. The insulating material 130 may be any suitable material, such as an interlayer dielectric (ILD). Examples of the insulating material 130 may include silicon oxide, silicon nitride, aluminum oxide, carbon-doped oxide, and/or silicon oxynitride. As known in the art of integrated circuit manufacturing, conductive vias and lines may be formed in an iterative process in which layers of structures are formed on top of each other. In some embodiments, the conductive vias 120/122/136/123 may have a width that is 20 nanometers or greater at their widest point (e.g., 30 nanometers), and a pitch of 80 nanometers or greater (e.g., 100 nanometers). In some embodiments, conductive lines (not shown) included in the quantum dot device 100 may have a width that is 100 nanometers or greater, and a pitch of 100 nanometers or greater. The particular arrangement of conductive vias shown in FIGS. 1-4 is simply illustrative, and any electrical routing arrangement may be implemented.

As discussed above, the structure of the trench 104-1 may be the same as the structure of the trench 104-2; similarly, the construction of gates 106/108 in and around the trench 104-1 may be the same as the construction of gates 106/108 in and around the trench 104-2. The gates 106/108 associated with the trench 104-1 may be mirrored by corresponding gates 106/108 associated with the parallel trench 104-2, and the insulating material 130 may separate the gates 106/108 associated with the different trenches 104-1 and 104-2. In particular, quantum dots 142 formed in the quantum well stack 146 under the trench 104-1 (under the gates 106/108) may have counterpart quantum dots 142 in the quantum well stack 146 under the trench 104-2 (under the corresponding gates 106/108). In some embodiments, the quantum dots 142 under the trench 104-1 may be used as “active” quantum dots in the sense that these quantum dots 142 act as qubits and are controlled (e.g., by voltages applied to the gates 106/108 associated with the trench 104-1) to perform quantum computations. The quantum dots 142 associated with the trench 104-2 may be used as “read” quantum dots in the sense that these quantum dots 142 may sense the quantum state of the quantum dots 142 under the trench 104-1 by detecting the electric field generated by the charge in the quantum dots 142 under the trench 104-1, and may convert the quantum state of the quantum dots 142 under the trench 104-1 into electrical signals that may be detected by the gates 106/108 associated with the trench 104-2. Each quantum dot 142 under the trench 104-1 may be read by its corresponding quantum dot 142 under the trench 104-2. Thus, the quantum dot device 100 enables both quantum computation and the ability to read the results of a quantum computation.

The quantum dot devices 100 disclosed herein may be manufactured using any suitable techniques. FIGS. 5-44 illustrate various example stages in the manufacture of the quantum dot device 100 of FIGS. 1-4 , in accordance with various embodiments. Although the particular manufacturing operations discussed below with reference to FIGS. 5-44 are illustrated as manufacturing a particular embodiment of the quantum dot device 100, these operations may be applied to manufacture many different embodiments of the quantum dot device 100, as discussed herein. Any of the elements discussed below with reference to FIGS. 5-44 may take the form of any of the embodiments of those elements discussed above (or otherwise disclosed herein).

FIG. 5 illustrates a cross-sectional view of an assembly 200 including a base 102. As discussed below, the base 102 may serve as a platform on which to form a quantum well stack 146. In some embodiments, the base 102 may include any suitable semiconductor material or materials. For example, the base 102 may include silicon (e.g., may be formed from a silicon wafer), germanium, or any other suitable material.

FIG. 6 illustrates a cross-sectional view of an assembly 202 subsequent to forming a quantum well stack 146 on the base 102 of the assembly 200 (FIG. 5 ). The quantum well stack 146 may include a quantum well layer (not shown) in which a 2DEG may form during operation of the quantum dot device 100. The one or more layers of the quantum well stack 146 may be formed by epitaxy. Various embodiments of the quantum well stack 146 are discussed below with reference to FIGS. 50-52 .

FIG. 7 is a cross-sectional view of an assembly 204 subsequent to providing a layer of gate dielectric 114 on the quantum well stack 146 of the assembly 202 (FIG. 6 ). In some embodiments, the gate dielectric 114 may be provided by atomic layer deposition (ALD), or any other suitable technique.

FIG. 8 is a cross-sectional view of an assembly 206 subsequent to providing a first gate metal layer 110A on the assembly 204 (FIG. 7 ). As shown in FIG. 8 , the first gate metal layer 110A may be blanket-deposited on the assembly 204. The deposition of the first gate metal layer 110A may utilize any suitable technique, such as ALD, CVD, or physical vapor deposition (PVD). In some embodiments, the first gate metal layer 110A may have a microstructure that includes columnar grains.

FIG. 9 is a cross-sectional view of an assembly 208 subsequent to etching the first gate metal layer 110A of the assembly 206 (FIG. 8 ), depositing insulating material 128 on and around the remaining first gate metal layer 110A, and then polishing back the insulating material 128 that extends above the first gate metal layer 110A (e.g., using a chemical mechanical polishing (CMP) technique) so that a top surface of the first gate metal layer 110A is coplanar with a top surface of the insulating material 128. Any suitable conventional lithographic process known in the art may be used to pattern the first gate metal layer 110A. For example, a hardmask may be provided on the first gate metal layer 110A, and a photoresist may be provided on the hardmask; the photoresist may be patterned to identify the areas of the first gate metal layer 110A that are to remain (corresponding to the areas in which the trenches 104 are to be formed, as discussed below), the hardmask may be etched in accordance with the patterned photoresist, and the first gate metal layer 110A may be etched in accordance with the etched hardmask (after which the remaining hardmask and photoresist may be removed). The etching of the first gate metal layer 110A may result in the patterning of the first gate metal layer 110A into volumes corresponding to the trenches 104; in other words, the first gate metal layer 110A may fill the trenches 104 in the insulating material 128 in the assembly 208. Subtractively patterning the first gate metal layer 110A, as illustrated in FIGS. 8 and 9 , may result in fewer defects in the first gate metal layer 110A than would be achievable by subtractively patterning the trenches 104 into the insulating material 128, and then filling the trenches 104 with the first gate metal layer 110A. Any suitable material may be used as the insulating material 128 to electrically insulate the trenches 104 from each other, as discussed above. As noted above, in some embodiments, the insulating material 128 may be a dielectric material, such as silicon oxide. FIG. 10 is a view of the assembly 208 taken along the section A-A of FIG. 9 , through a trench 104 (while FIG. 9 illustrates the assembly 208 taken along the section D-D of FIG. 10 ). FIGS. 11-14 maintain the perspective of FIG. 10 .

FIG. 11 is a cross-sectional view of an assembly 210 subsequent to providing a second gate metal layer 110B and a hardmask 116 on the assembly 208 (FIGS. 9-10 ). The hardmask 116 may be formed of an electrically insulating material, such as silicon nitride or carbon-doped nitride. The second gate metal layer 110B of the assembly 210 may extend over the insulating material 128 and the first gate metal layer 110A, as shown.

FIG. 12 is a cross-sectional view of an assembly 212 subsequent to patterning the hardmask 116 of the assembly 210 (FIG. 11 ). The pattern applied to the hardmask 116 may correspond to the locations for the gates 106, as discussed below. The hardmask 116 may be patterned by applying a resist, patterning the resist using lithography, and then etching the hardmask (using dry etching or any appropriate technique).

FIG. 13 is a cross-sectional view of an assembly 214 subsequent to etching the assembly 212 (FIG. 12 ) to remove the gate metal 110 (i.e., the first gate metal layer 110A and the second gate metal layer 110B) that is not protected by the patterned hardmask 116 to form the gates 106. The etching of the gate metal 110 may form multiple gates 106 associated with a particular trench 104, and also separate portions of gate metal 110 corresponding to gates 106 associated with different trenches 104 (e.g., as illustrated in FIG. 1 ). In some embodiments, as illustrated in FIG. 13 , the gate dielectric 114 may remain on the quantum well stack 146 after the etched gate metal 110 is etched away; in other embodiments, the gate dielectric 114 may also be etched during the etching of the gate metal 110. Examples of such embodiments are discussed below with reference to FIGS. 56-59 .

FIG. 14 is a cross-sectional view of an assembly 216 subsequent to providing spacer material 132 on the assembly 214 (FIG. 13 ). FIG. 15 is a view of the assembly 216 taken along the section D-D of FIG. 14 , through the region between adjacent gates 106 (while FIG. 14 illustrates the assembly 216 taken along the section A-A of FIG. 15 , along a trench 104). The spacer material 132 may include any of the materials discussed above with reference to the spacers 134, for example, and may be deposited using any suitable technique. For example, the spacer material 132 may be a nitride material (e.g., silicon nitride) deposited by CVD or ALD. As illustrated in FIGS. 14 and 15 , the spacer material 132 may be conformally deposited on the assembly 214.

FIG. 16 is a cross-sectional view of an assembly 218 subsequent to providing capping material 133 on the assembly 216 (FIGS. 14 and 15 ). FIG. 17 is a view of the assembly 218 taken along the section D-D of FIG. 16 , through the region between adjacent gates 106 (while FIG. 16 illustrates the assembly 218 taken along the section A-A of FIG. 17 , along a trench 104). The capping material 133 may be any suitable material; for example, the capping material 133 may be silicon oxide deposited by CVD or ALD. As illustrated in FIGS. 16 and 17 , the capping material 133 may be conformally deposited on the assembly 216.

FIG. 18 is a cross-sectional view of an assembly 220 subsequent to providing a sacrificial material 135 on the assembly 218 (FIGS. 16 and 17 ). FIG. 19 is a view of the assembly 220 taken along the section D-D of FIG. 18 , through the region between adjacent gates 106 (while FIG. 18 illustrates the assembly 220 taken along the section A-A of FIG. 19 , through a trench 104). The sacrificial material 135 may be deposited on the assembly 218 to completely cover the capping material 133, then the sacrificial material 135 may be recessed to expose portions 137 of the capping material 133. In particular, the portions 137 of capping material 133 disposed near the hardmask 116 on the gate metal 110 may not be covered by the sacrificial material 135. As illustrated in FIG. 19 , all of the capping material 133 disposed in the region between adjacent gates 106 may be covered by the sacrificial material 135. The recessing of the sacrificial material 135 may be achieved by any etching technique, such as a dry etch. The sacrificial material 135 may be any suitable material, such as a bottom anti-reflective coating (BARC).

FIG. 20 is a cross-sectional view of an assembly 222 subsequent to treating the exposed portions 137 of the capping material 133 of the assembly 220 (FIGS. 18 and 19 ) to change the etching characteristics of the exposed portions 137 relative to the rest of the capping material 133. FIG. 21 is a view of the assembly 222 taken along the section D-D of FIG. 20 , through the region between adjacent gates 106 (while FIG. 20 illustrates the assembly 222 taken along the section A-A of FIG. 21 , through a trench 104). In some embodiments, this treatment may include performing a high-dose ion implant in which the implant dose is high enough to cause a compositional change in the portions 137 and achieve a desired change in etching characteristics.

FIG. 22 is a cross-sectional view of an assembly 224 subsequent to removing the sacrificial material 135 and the unexposed capping material 133 of the assembly 222 (FIGS. 20 and 21 ). FIG. 23 is a view of the assembly 224 taken along the section D-D of FIG. 22 , through the region between adjacent gates 106 (while FIG. 22 illustrates the assembly 224 taken along the section A-A of FIG. 23 , through a trench 104). The sacrificial material 135 may be removed using any suitable technique (e.g., by ashing, followed by a cleaning step), and the untreated capping material 133 may be removed using any suitable technique (e.g., by etching). In embodiments in which the capping material 133 is treated by ion implantation (e.g., as discussed above with reference to FIGS. 20 and 21 ), a high temperature anneal may be performed to incorporate the implanted ions in the portions 137 of the capping material 133 before removing the untreated capping material 133. The remaining treated capping material 133 in the assembly 224 may provide capping structures 145 disposed proximate to the “tops” of the gates 106 and extending over the spacer material 132 disposed on the “sides” of the gates 106.

FIG. 24 is a cross-sectional view of an assembly 226 subsequent to directionally etching the spacer material 132 of the assembly 224 (FIGS. 22 and 23 ) that isn't protected by a capping structure 145, leaving spacer material 132 on the sides and top of the gates 106 (e.g., on the sides and top of the hardmask 116 and the gate metal 110). FIG. 25 is a view of the assembly 226 taken along the section D-D of FIG. 24 , through the region between adjacent gates 106 (while FIG. 24 illustrates the assembly 226 taken along the section A-A of FIG. 25 , through a trench 104). The etching of the spacer material 132 may be an anisotropic etch, etching the spacer material 132 “downward” to remove the spacer material 132 in some of the area between the gates 106 (as illustrated in FIGS. 24 and 25 ), while leaving the spacer material 132 on the sides and tops of the gates 106. In some embodiments, the anisotropic etch may be a dry etch. FIGS. 26-35 maintain the cross-sectional perspective of FIG. 24 .

FIG. 26 is a cross-sectional view of an assembly 228 subsequent to removing the capping structures 145 from the assembly 226 (FIGS. 24 and 25 ). The capping structures 145 may be removed using any suitable technique (e.g., a wet etch). The spacer material 132 that remains in the assembly 228 may include spacers 134 disposed on the sides of the gates 106, and spacer material portions 139 disposed on the top of the gates 106.

FIG. 27 is a cross-sectional view of an assembly 230 subsequent to providing the gate metal 112 on the assembly 228 (FIG. 26 ). The gate metal 112 may fill the areas between adjacent ones of the gates 106, and may extend over the tops of the gates 106 and over the spacer material portions 139. The gate metal 112 of the assembly 230 may fill the trenches 104 (between the gates 106) and extend over the insulating material 128.

FIG. 28 is a cross-sectional view of an assembly 232 subsequent to planarizing the assembly 230 (FIG. 27 ) to remove the gate metal 112 above the gates 106, as well as to remove the spacer material portions 139 above the hardmask 116. In some embodiments, the assembly 230 may be planarized using a CMP technique. The planarizing of the assembly 230 may also remove some of the hardmask 116, in some embodiments. Some of the remaining gate metal 112 may fill the areas between adjacent ones of the gates 106, while other portions 150 of the remaining gate metal 112 may be located “outside” of the gates 106.

FIG. 29 is a cross-sectional view of an assembly 234 subsequent to providing a hardmask 118 on the planarized surface of the assembly 232 (FIG. 28 ). The hardmask 118 may be formed of any of the materials discussed above with reference to the hardmask 116, for example.

FIG. 30 is a cross-sectional view of an assembly 236 subsequent to patterning the hardmask 118 of the assembly 234 (FIG. 29 ). The pattern applied to the hardmask 118 may extend over the hardmask 116 (and over the gate metal 110 of the gates 106, as well as over the locations for the gates 108, as illustrated in FIG. 2 ). The hardmask 118 may be non-coplanar with the hardmask 116, as illustrated in FIG. 30 . The hardmask 118 illustrated in FIG. 30 may thus be a common, continuous portion of hardmask 118 that extends over all of the hardmask 116. The hardmask 118 may be patterned using any of the techniques discussed above with reference to the patterning of the hardmask 116, for example.

FIG. 31 is a cross-sectional view of an assembly 238 subsequent to etching the assembly 236 (FIG. 30 ) to remove the portions 150 that are not protected by the patterned hardmask 118 to form the gates 108. Portions of the hardmask 118 may remain on top of the hardmask 116, as shown. The operations performed on the assembly 236 may include removing any gate dielectric 114 that is “exposed” on the quantum well stack 146, as shown. The excess gate dielectric 114 may be removed using any suitable technique, such as chemical etching or silicon bombardment. In some embodiments, the patterned hardmask 118 may extend “laterally” beyond the gates 106 to cover gate metal 112 that it located “outside” the gates 106. In such embodiments, those portions of gate metal 112 may remain in the assembly 238 and may provide the outermost gates (i.e., those gates 108 may bookend the other gates 106/108). The exposed gate metal 112 at the sides of those outer gates 108 may be insulated by additional spacers 134, formed using any of the techniques discussed herein. Such outer gates 108 may be included in any of the embodiments disclosed herein.

FIG. 32 is a cross-sectional view of an assembly 240 subsequent to doping the quantum well stack 146 of the assembly 238 (FIG. 31 ) to form doped regions 140 in the portions of the quantum well stack 146 “outside” of the gates 106/108. The type of dopant used to form the doped regions 140 may depend on the type of quantum dot desired, as discussed above. In some embodiments, the doping may be performed by ion implantation. For example, when the quantum dot 142 is to be an electron-type quantum dot 142, the doped regions 140 may be formed by ion implantation of phosphorous, arsenic, or another n-type material. When the quantum dot 142 is to be a hole-type quantum dot 142, the doped regions 140 may be formed by ion implantation of boron or another p-type material. An annealing process that activates the dopants and causes them to diffuse farther into the quantum well stack 146 may follow the ion implantation process. The depth of the doped regions 140 may take any suitable value; for example, in some embodiments, the doped regions 140 may extend into the quantum well stack 146 to a depth 115 between 500 Angstroms and 1000 Angstroms.

The outer spacers 134 on the outer gates 106 may provide a doping boundary, limiting diffusion of the dopant from the doped regions 140 into the area under the gates 106/108. As shown, the doped regions 140 may extend under the adjacent outer spacers 134. In some embodiments, the doped regions 140 may extend past the outer spacers 134 and under the gate metal 110 of the outer gates 106, may extend only to the boundary between the outer spacers 134 and the adjacent gate metal 110, or may terminate under the outer spacers 134 and not reach the boundary between the outer spacers 134 and the adjacent gate metal 110. Examples of such embodiments are discussed below with reference to FIGS. 53 and 54 . The doping concentration of the doped regions 140 may, in some embodiments, be between 10¹⁷/cm³ and 10²⁰/cm³.

FIG. 33 is a cross-sectional side view of an assembly 242 subsequent to providing a layer of nickel or other material 143 over the assembly 240 (FIG. 32 ). The nickel or other material 143 may be deposited on the assembly 240 using any suitable technique (e.g., a plating technique, CVD, or ALD).

FIG. 34 is a cross-sectional side view of an assembly 244 subsequent to annealing the assembly 242 (FIG. 33 ) to cause the material 143 to interact with the doped regions 140 to form the interface material 141, then removing the unreacted material 143. When the doped regions 140 include silicon and the material 143 includes nickel, for example, the interface material 141 may be nickel silicide. Materials other than nickel may be deposited in the operations discussed above with reference to FIG. 33 in order to form other interface materials 141, including titanium, aluminum, molybdenum, cobalt, tungsten, or platinum, for example. More generally, the interface material 141 of the assembly 244 may include any of the materials discussed herein with reference to the interface material 141.

FIG. 35 is a cross-sectional view of an assembly 246 subsequent to providing an insulating material 130 on the assembly 244 (FIG. 34 ). FIG. 36 is another cross-sectional view of the assembly 246, taken along the section C-C of FIG. 35 (while the cross-sectional view of FIG. 35 is taken along the section A-A of FIG. 36 ). The insulating material 130 may take any of the forms discussed above. For example, the insulating material 130 may be a dielectric material, such as silicon oxide. The insulating material 130 may be provided on the assembly 244 using any suitable technique, such as spin coating, CVD, or plasma-enhanced CVD (PECVD). In some embodiments, the insulating material 130 may be polished back after deposition, and before further processing. In some embodiments, the thickness 131 of the insulating material 130 in the assembly 246 (as measured from the hardmask 118, as indicated in FIG. 35 ) may be between 50 nanometers and 1.2 microns (e.g., between 50 nanometers and 300 nanometers). In some embodiments, a nitride etch stop layer (NESL) may be provided on the assembly 244 (e.g., above the interface material 141) before providing the insulating material 130.

FIG. 37 is a cross-sectional view of an assembly 248 subsequent to forming a trench 125 in the insulating material 130 of the assembly 246 (FIGS. 35 and 36 ). The trench 125 may be formed using any desired techniques (e.g., resist patterning followed by etching), and may have a depth 127 and a width 129 that may take the form of any of the embodiments of the thickness 169 and the width 171, respectively, discussed above with reference to the magnet line 121. FIG. 38 is another cross-sectional view of the assembly 248, taken along the section C-C of FIG. 37 (while the cross-sectional view of FIG. 37 is taken along the section A-A of FIG. 38 ). In some embodiments, the assembly 246 may be planarized to remove the hardmasks 116 and 118, then additional insulating material 130 may be provided on the planarized surface before forming the trench 125; in such an embodiment, the hardmasks 116 and 118 would not be present in the quantum dot device 100.

FIG. 39 is a cross-sectional view of an assembly 250 subsequent to filling the trench 125 of the assembly 248 (FIGS. 37 and 38 ) with a material to form the magnet line 121. The magnet line 121 may be formed using any desired techniques (e.g., plating followed by planarization, or a semi-additive process), and may take the form of any of the embodiments disclosed herein. FIG. 40 is another cross-sectional view of the assembly 250, taken along the section C-C of FIG. 39 (while the cross-sectional view of FIG. 39 is taken along the section A-A of FIG. 40 ).

FIG. 41 is a cross-sectional view of an assembly 252 subsequent to providing additional insulating material 130 on the assembly 250 (FIGS. 39 and 40 ). The insulating material 130 provided on the assembly 250 may take any of the forms of the insulating material 130 discussed above. FIG. 42 is another cross-sectional view of the assembly 252, taken along the section C-C of FIG. 41 (while the cross-sectional view of FIG. 41 is taken along the section A-A of FIG. 42 ).

FIG. 43 is a cross-sectional view of an assembly 254 subsequent to forming, in the assembly 252 (FIGS. 41 and 42 ), conductive vias 120 through the insulating material 130 (and the hardmasks 116 and 118) to contact the gate metal 110 of the gates 106, conductive vias 122 through the insulating material 130 (and the hardmask 118) to contact the gate metal 112 of the gates 108, conductive vias 136 through the insulating material 130 to contact the interface material 141 of the doped regions 140, and conductive vias 123 through the insulating material 130 to contact the magnet line 121. Further conductive vias and/or lines may be formed in the assembly 254 using conventional interconnect techniques, if desired. The resulting assembly 254 may take the form of the quantum dot device 100 discussed above with reference to FIGS. 1-4 . FIG. 44 is another cross-sectional view of the assembly 254, taken along the section C-C of FIG. 43 (while the cross-sectional view of FIG. 43 is taken along the section A-A of FIG. 44 ).

In the embodiment of the quantum dot device 100 illustrated in FIGS. 1-4 , the magnet line 121 is oriented parallel to the longitudinal axes of the trenches 104. In other embodiments, the magnet line 121 may not be oriented parallel to the longitudinal axes of the trenches 104. For example, FIGS. 45-47 are various cross-sectional views of an embodiment of a quantum dot device 100 having multiple magnet lines 121, each proximate to the trenches 104 and oriented perpendicular to the longitudinal axes of the trenches 104. Other than orientation, the magnet lines 121 of the embodiment of FIGS. 45-47 may take the form of any of the embodiments of the magnet line 121 discussed above. The other elements of the quantum dot devices 100 of FIGS. 45-47 may take the form of any of those elements discussed herein. The manufacturing operations discussed above with reference to FIGS. 5-44 may be used to manufacture the quantum dot device 100 of FIGS. 45-47 .

Although a single magnet line 121 is illustrated in FIGS. 1-4 , multiple magnet lines 121 may be included in that embodiment of the quantum dot device 100 (e.g., multiple magnet lines 121 parallel to the longitudinal axes of the trenches 104). For example, the quantum dot device 100 of FIGS. 1-4 may include a second magnet line 121 proximate to the trench 104-2 in a symmetric manner to the magnet line 121 illustrated proximate to the trench 104-1. In some embodiments, multiple magnet lines 121 may be included in a quantum dot device 100, and these magnet lines 121 may or may not be parallel to one another. For example, in some embodiments, a quantum dot device 100 may include two (or more) magnet lines 121 that are oriented perpendicular to each other.

As discussed above, in the embodiment illustrated in FIG. 3 (and FIGS. 5-44 ), there may not be any substantial spacer material between the gate metal 112 and the proximate sidewalls of the trench 104 in the y-direction. In other embodiments, spacers 134 may also be disposed between the gate metal 112 and the sidewalls of the trench 104 in the y-direction. A cross-sectional view of such an embodiment is shown in FIG. 48 (analogous to the cross-sectional view of FIG. 3 ). To manufacture such a quantum dot device 100, the operations discussed above with reference to FIGS. 16-25 may not be performed; instead, the spacer material 132 of the assembly 216 of FIGS. 14 and 15 may be anisotropically etched (as discussed with reference to FIGS. 24 and 25 ) to form the spacers 134 on the sides of the gates 106 and on the sidewalls of the trench 104. FIG. 49 is a cross-sectional view of an assembly 256 that may be formed by such a process (taking the place of the assembly 226 of FIG. 25 ); the view along the section A-A of the assembly 256 may be similar to FIG. 26 , but may not include the spacer material portions 139. The assembly 256 may be further processed as discussed above with reference to FIGS. 27-44 (or other embodiments discussed herein) to form a quantum dot device 100.

As discussed above, the quantum well stack 146 may include a quantum well layer in which a 2DEG may form during operation of the quantum dot device 100. The quantum well stack 146 may take any of a number of forms, several of which are illustrated in FIGS. 50-52 . The various layers in the quantum well stacks 146 discussed below may be grown on the base 102 (e.g., using epitaxial processes).

Although the singular term “layer” may be used to refer to various components of the quantum well stacks 146 of FIGS. 50-52 , any of the layers discussed below may include multiple materials arranged in any suitable manner. In embodiments in which a quantum well stack 146 includes layers other than a quantum well layer 152, layers other than the quantum well layer 152 in a quantum well stack 146 may have higher threshold voltages for conduction than the quantum well layer 152 so that when the quantum well layer 152 is biased at its threshold voltages, the quantum well layer 152 conducts and the other layers of the quantum well stack 146 do not. This may avoid parallel conduction in both the quantum well layer 152 and the other layers, and thus avoid compromising the strong mobility of the quantum well layer 152 with conduction in layers having inferior mobility. In some embodiments, silicon used in a quantum well stack 146 (e.g., in a quantum well layer 152) may be grown from precursors enriched with the 28Si isotope. In some embodiments, germanium used in a quantum well stack 146 (e.g., in a quantum well layer 152) may be grown from precursors enriched with the 70Ge, 72Ge, or 74Ge isotope.

FIG. 50 is a cross-sectional view of a quantum well stack 146 including only a quantum well layer 152. The quantum well layer 152 may be disposed on the base 102 (e.g., as discussed above with reference to FIG. 6 ), and may be formed of a material such that, during operation of the quantum dot device 100, a 2DEG may form in the quantum well layer 152 proximate to the upper surface of the quantum well layer 152. The gate dielectric 114 of the gates 106/108 may be disposed on the upper surface of the quantum well layer 152 (e.g., as discussed above with reference to FIG. 7 ). In some embodiments, the quantum well layer 152 of FIG. 50 may be formed of intrinsic silicon, and the gate dielectric 114 may be formed of silicon oxide; in such an arrangement, during use of the quantum dot device 100, a 2DEG may form in the intrinsic silicon at the interface between the intrinsic silicon and the silicon oxide. Embodiments in which the quantum well layer 152 of FIG. 50 is formed of intrinsic silicon may be particularly advantageous for electron-type quantum dot devices 100. In some embodiments, the quantum well layer 152 of FIG. 50 may be formed of intrinsic germanium, and the gate dielectric 114 may be formed of germanium oxide; in such an arrangement, during use of the quantum dot device 100, a 2DEG may form in the intrinsic germanium at the interface between the intrinsic germanium and the germanium oxide. Such embodiments may be particularly advantageous for hole-type quantum dot devices 100. In some embodiments, the quantum well layer 152 may be strained, while in other embodiments, the quantum well layer 152 may not be strained. The thicknesses (i.e., z-heights) of the layers in the quantum well stack 146 of FIG. 50 may take any suitable values. For example, in some embodiments, the thickness of the quantum well layer 152 (e.g., intrinsic silicon or germanium) may be between 0.8 microns and 1.2 microns.

FIG. 51 is a cross-sectional view of a quantum well stack 146 including a quantum well layer 152 and a barrier layer 154. The quantum well stack 146 may be disposed on the base 102 (e.g., as discussed above with reference to FIG. 6 ) such that the barrier layer 154 is disposed between the quantum well layer 152 and the base 102. The barrier layer 154 may provide a potential barrier between the quantum well layer 152 and the base 102. As discussed above with reference to FIG. 50 , the quantum well layer 152 of FIG. 51 may be formed of a material such that, during operation of the quantum dot device 100, a 2DEG may form in the quantum well layer 152 proximate to the upper surface of the quantum well layer 152. For example, in some embodiments in which the base 102 is formed of silicon, the quantum well layer 152 of FIG. 51 may be formed of silicon, and the barrier layer 154 may be formed of silicon germanium. The germanium content of this silicon germanium may be 20-80% (e.g., 30%). In some embodiments in which the quantum well layer 152 is formed of germanium, the barrier layer 154 may be formed of silicon germanium (with a germanium content of 20-80% (e.g., 70%)). The thicknesses (i.e., z-heights) of the layers in the quantum well stack 146 of FIG. 51 may take any suitable values. For example, in some embodiments, the thickness of the barrier layer 154 (e.g., silicon germanium) may be between 0 nanometers and 400 nanometers. In some embodiments, the thickness of the quantum well layer 152 (e.g., silicon or germanium) may be between 5 nanometers and 30 nanometers.

FIG. 52 is a cross-sectional view of a quantum well stack 146 including a quantum well layer 152 and a barrier layer 154-1, as well as a buffer layer 176 and an additional barrier layer 154-2. The quantum well stack 146 may be disposed on the base 102 (e.g., as discussed above with reference to FIG. 6 ) such that the buffer layer 176 is disposed between the barrier layer 154-1 and the base 102. The buffer layer 176 may be formed of the same material as the barrier layer 154, and may be present to trap defects that form in this material as it is grown on the base 102. In some embodiments, the buffer layer 176 may be grown under different conditions (e.g., deposition temperature or growth rate) from the barrier layer 154-1. In particular, the barrier layer 154-1 may be grown under conditions that achieve fewer defects than the buffer layer 176. In some embodiments in which the buffer layer 176 includes silicon germanium, the silicon germanium of the buffer layer 176 may have a germanium content that varies from the base 102 to the barrier layer 154-1; for example, the silicon germanium of the buffer layer 176 may have a germanium content that varies from zero percent at the silicon base 102 to a nonzero percent (e.g., 30%) at the barrier layer 154-1. The thicknesses (i.e., z-heights) of the layers in the quantum well stack 146 of FIG. 52 may take any suitable values. For example, in some embodiments, the thickness of the buffer layer 176 (e.g., silicon germanium) may be between 0.3 microns and 4 microns (e.g., 0.3 microns-2 microns, or 0.5 microns). In some embodiments, the thickness of the barrier layer 154-1 (e.g., silicon germanium) may be between 0 nanometers and 400 nanometers. In some embodiments, the thickness of the quantum well layer 152 (e.g., silicon or germanium) may be between 5 nanometers and 30 nanometers (e.g., 10 nanometers). The barrier layer 154-2, like the barrier layer 154-1, may provide a potential energy barrier around the quantum well layer 152, and may take the form of any of the embodiments of the barrier layer 154-1. In some embodiments, the thickness of the barrier layer 154-2 (e.g., silicon germanium) may be between 25 nanometers and 75 nanometers (e.g., 32 nanometers).

As discussed above with reference to FIG. 51 , the quantum well layer 152 of FIG. 52 may be formed of a material such that, during operation of the quantum dot device 100, a 2DEG may form in the quantum well layer 152 proximate to the upper surface of the quantum well layer 152. For example, in some embodiments in which the base 102 is formed of silicon, the quantum well layer 152 of FIG. 52 may be formed of silicon, and the barrier layer 154-1 and the buffer layer 176 may be formed of silicon germanium. In some such embodiments, the silicon germanium of the buffer layer 176 may have a germanium content that varies from the base 102 to the barrier layer 154-1; for example, the silicon germanium of the buffer layer 176 may have a germanium content that varies from zero percent at the silicon base 102 to a nonzero percent (e.g., 30%) at the barrier layer 154-1. In other embodiments, the buffer layer 176 may have a germanium content equal to the germanium content of the barrier layer 154-1 but may be thicker than the barrier layer 154-1 so as to absorb the defects that arise during growth.

In some embodiments, the quantum well layer 152 of FIG. 52 may be formed of germanium, and the buffer layer 176 and the barrier layer 154-1 may be formed of silicon germanium. In some such embodiments, the silicon germanium of the buffer layer 176 may have a germanium content that varies from the base 102 to the barrier layer 154-1; for example, the silicon germanium of the buffer layer 176 may have a germanium content that varies from zero percent at the base 102 to a nonzero percent (e.g., 70%) at the barrier layer 154-1. The barrier layer 154-1 may in turn have a germanium content equal to the nonzero percent. In other embodiments, the buffer layer 176 may have a germanium content equal to the germanium content of the barrier layer 154-1 but may be thicker than the barrier layer 154-1 so as to absorb the defects that arise during growth. In some embodiments of the quantum well stack 146 of FIG. 52 , the buffer layer 176 and/or the barrier layer 154-2 may be omitted.

As discussed above with reference to FIGS. 2 and 32 , the outer spacers 134 on the outer gates 106 may provide a doping boundary, limiting diffusion of the dopant from the doped regions 140 into the area under the gates 106/108. In some embodiments, the doped regions 140 may extend past the outer spacers 134 and under the outer gates 106. For example, as illustrated in FIG. 53, the doped region 140 may extend past the outer spacers 134 and under the outer gates 106 by a distance 182 between 0 nanometers and 10 nanometers. In some embodiments, the doped regions 140 may not extend past the outer spacers 134 toward the outer gates 106, but may instead “terminate” under the outer spacers 134. For example, as illustrated in FIG. 54 , the doped regions 140 may be spaced away from the interface between the outer spacers 134 and the outer gates 106 by a distance 184 between 0 nanometers and 10 nanometers. The interface material 141 is omitted from FIGS. 53 and 54 for ease of illustration.

As noted above, a quantum dot device 100 may include multiple trenches 104 arranged in an array of any desired size. For example, FIG. 55A is a top cross-sectional view, like the view of FIG. 4 , of a quantum dot device 100 having multiple trenches 104 arranged in a two-dimensional array. In the particular example illustrated in FIG. 55A, the trenches 104 may be arranged in pairs, each pair including an “active” trench 104 and a “read” trench 104, as discussed above. The particular number and arrangement of trenches 104 in FIG. 55A is simply illustrative, and any desired arrangement may be used.

As noted above, a single trench 104 may include multiple groups of gates 106/108, spaced apart along the trench by a doped region 140. FIG. 55B is a cross-sectional view of an example of such a quantum dot device 100 having multiple groups of gates 180 at least partially disposed in a single trench 104 above a quantum well stack 146, in accordance with various embodiments. Each of the groups 180 may include gates 106/108 (not labeled in FIG. 55B for ease of illustration) that may take the form of any of the embodiments of the gates 106/108 discussed herein. A doped region 140 (and its interface material 141) may be disposed between two adjacent groups 180 (labeled in FIG. 55B as groups 180-1 and 180-2), and may provide a common reservoir for both groups 180. In some embodiments, this “common” doped region 140 may be electrically contacted by a single conductive via 136. The particular number of gates 106/108 illustrated in FIG. 55B, and the particular number of groups 180, is simply illustrative, and a trench 104 may include any suitable number of gates 106/108 arranged in any suitable number of groups 180. The quantum dot device 100 of FIG. 55B may also include one or more magnet lines 121, arranged as desired.

As discussed above with reference to FIGS. 1-4 , in some embodiments in which the gate dielectric 114 is not a layer shared commonly between the gates 108 and 106, but instead is separately deposited on the trench 104 between the spacers 134, the gate dielectric 114 may extend at least partially up the sides of the spacers 134, and the gate metal 112 may extend between the portions of gate dielectric 114 on the spacers 134. FIGS. 56-59 illustrate various alternative stages in the manufacture of such an embodiment of a quantum dot device 100, in accordance with various embodiments. In particular, the operations illustrated in FIGS. 56-59 (as discussed below) may take the place of the operations illustrated in FIGS. 13-27 .

FIG. 56 is a cross-sectional view of an assembly 258 subsequent to etching the assembly 212 (FIG. 12 ) to remove the gate metal 110, and the gate dielectric 114 that is not protected by the patterned hardmask 116, to form the gates 106.

FIG. 57 is a cross-sectional view of an assembly 260 subsequent to providing spacers 134 on the sides of the gates 106 (e.g., on the sides of the hardmask 116, the gate metal 110, and the gate dielectric 114) and spacer material portions 139 above the gates 106 (e.g., on the hardmask 116) of the assembly 258 (FIG. 56 ). The provision of the spacer material portions 139/spacers 134 may take any of the forms discussed above with reference to FIG. 14-26 or 48 , for example.

FIG. 58 is a cross-sectional view of an assembly 262 subsequent to providing a gate dielectric 114 in the trench 104 between the gates 106 of the assembly 260 (FIG. 57 ). In some embodiments, the gate dielectric 114 provided between the gates 106 of the assembly 260 may be formed by ALD and, as illustrated in FIG. 58 , may cover the exposed quantum well stack 146 between the gates 106, and may extend onto the adjacent spacers 134.

FIG. 59 is a cross-sectional view of an assembly 264 subsequent to providing the gate metal 112 on the assembly 262 (FIG. 58 ). The gate metal 112 may fill the areas in the trench 104 between adjacent ones of the gates 106, and may extend over the tops of the gates 106, as shown. The provision of the gate metal 112 may take any of the forms discussed above with reference to FIG. 27 , for example. The assembly 264 may be further processed as discussed above with reference to FIGS. 28-44 .

In some embodiments, techniques for depositing the gate dielectric 114 and the gate metal 112 for the gates 108 like those illustrated in FIGS. 58-59 may be used to form the gates 108 using alternative manufacturing steps to those illustrated in FIGS. 27-34 . For example, the insulating material 130 may be deposited on the assembly 228 (FIG. 26 ), the insulating material 130 may be “opened” to expose the areas in which the gates 108 are to be disposed, a layer of gate dielectric 114 and gate metal 112 may be deposited on this structure to fill the openings (e.g., as discussed with reference to FIGS. 58-59 ), the resulting structure may be polished back to remove the excess gate dielectric 114 and gate metal 112 (e.g., as discussed above with reference to FIG. 28 ), the insulating material 130 at the sides of the outermost gates 106 may be opened to expose the quantum well stack 146, the exposed quantum well stack 146 may be doped and provided with an interface material 141 (e.g., as discussed above with reference to FIGS. 32-34 ), and the openings may be filled back in with insulating material 130 to form an assembly like the assembly 246 of FIGS. 35 and 36 . Further processing may be performed as described herein.

In the embodiment of FIGS. 1-3 , a gate 106 is spaced apart from an adjacent gate 108 by a spacer 134 that extends from the gate dielectric 114 to the full height of the gates 106/108. In other embodiments, a gate 106 may be spaced apart from an adjacent gate 108 by a stack of spacers 134, rather than a single spacer 134. For example, FIG. 60 is a side, cross-sectional view of a quantum dot device 100 that includes a stack of two spacers 134 between adjacent gates 106/108. FIG. 60 shares a perspective with FIG. 3 . The lower spacers 134-1 may be disposed in the trench 104, sandwiching portions of the first gate metal layer 110A, while the upper spacers 134-2 may be disposed above the first gate metal layer 110A, sandwiching portions of the second gate metal layer 110B, as shown. A quantum dot device 100 that includes such a stack of spacers 134 may be manufactured by patterning the first gate metal layer 110A of the assembly 208 (FIGS. 9 and 10 ) into portions corresponding to the gates 106, forming the lower spacers 134-1 on the sides of the patterned first gate metal layer 110A (e.g., in accordance with the process of FIGS. 14-26 ), filling the space between the portions of patterned first gate metal layer 110A/lower spacers 134-1 with a sacrificial material, blanket depositing and patterning the second gate metal layer 110B (e.g., in accordance with the process of FIGS. 11-13 , and then forming the upper spacers 134-2 on the sides of the patterned second gate metal layer 110B. The sacrificial material may be removed before depositing the gate metal 112 (and any additional gate dielectric 114, if such dielectric is to be deposited).

As noted above, in some embodiments, the gate metal 112 of the gates 108 may include multiple layers. For example, FIG. 61 is a side, cross-sectional view of a quantum dot device 100 in which the gate metal 112 is provided by a first gate metal layer 112A and a second gate metal layer 112B, analogous to the first gate metal layer 110A and the second gate metal layer 110B, respectively. The first gate metal layer 112A may be in the trench 104 and may have a top surface that is coplanar with a top surface of the insulating material 128, while the second gate metal layer 112B may be above the first gate metal layer 112A (as discussed above with reference to the first gate metal layer 110A and the second gate metal layer 110B). Any of the materials discussed above with reference to the gate metal 112 may be included in the first gate metal layer 112A and/or the second gate metal layer 112B. In some embodiments, the first gate metal layer 112A may have a different material composition than the second gate metal layer 112B. For example, the first gate metal layer 112A (the second gate metal layer 112B) may be titanium nitride, while the second gate metal layer 112B (the first gate metal layer 112A) may be a material different from titanium nitride. In some embodiments, the first gate metal layer 112A and the second gate metal layer 112B may have a same material composition, but may have a different microstructure. These different microstructures may arise, for example, by different deposition and/or patterning techniques used to form the first gate metal layer 112A and the second gate metal layer 112B. In some embodiments, a seam delineating the interface between the top surface of the first gate metal layer 112A and the bottom surface of the second gate metal layer 112B may be present in the quantum dot device 100. The quantum dot device 100 also includes stacks of spacers 134 between adjacent gates 106/108, as discussed above with reference to FIG. 60 .

A quantum dot device 100 like the one illustrated in FIG. 61 may be manufactured by patterning the first gate metal layer 110A of the assembly 208 (FIGS. 9 and 10 ) into portions corresponding to the gates 106, forming the lower spacers 134-1 on the sides of the patterned first gate metal layer 110A (e.g., in accordance with the process of FIGS. 14-26 ), filling the space between the portions of patterned first gate metal layer 110A/lower spacers 134-1 with the first gate metal layer 112A, blanket depositing and patterning the second gate metal layer 110B (e.g., in accordance with the process of FIGS. 11-13 , forming the upper spacers 134-2 on the sides of the patterned second gate metal layer 110B, and then filling the space between the portions of patterned second gate metal layer 110B/upper spacers 134-2 with the second gate metal layer 112B.

In some embodiments, the quantum dot device 100 may be included in a die and coupled to a package substrate to form a quantum dot device package. For example, FIG. 62 is a cross-sectional view of a die 302 including the quantum dot device 100 of FIG. 2 and conductive pathway layers 303 disposed thereon, while FIG. 63 is a cross-sectional view of a quantum dot device package 300 in which the die 302 and another die 350 are coupled to a package substrate 304 (e.g., in a system-on-a-chip (SoC) arrangement). Details of the quantum dot device 100 are omitted from FIG. 63 for economy of illustration. As noted above, the particular quantum dot device 100 illustrated in FIGS. 62 and 63 may take a form similar to the embodiment illustrated in FIG. 3 , but any of the quantum dot devices 100 disclosed herein may be included in a die (e.g., the die 302) and coupled to a package substrate (e.g., the package substrate 304). In particular, any number of trenches 104, gates 106/108, doped regions 140, magnet lines 121, and other components discussed herein with reference to various embodiments of the quantum dot device 100 may be included in the die 302.

The die 302 may include a first face 320 and an opposing second face 322. The base 102 may be proximate to the second face 322, and conductive pathways 315 from various components of the quantum dot device 100 may extend to conductive contacts 365 disposed at the first face 320. The conductive pathways 315 may include conductive vias, conductive lines, and/or any combination of conductive vias and lines. For example, FIG. 62 illustrates an embodiment in which one conductive pathway 315 (extending between a magnet line 121 and associated conductive contact 365) includes a conductive via 123, a conductive line 393, a conductive via 398, and a conductive line 396. More or fewer structures may be included in the conductive pathways 315, and analogous conductive pathways 315 may be provided between ones of the conductive contacts 365 and the gates 106/108, doped regions 140, or other components of the quantum dot device 100. In some embodiments, conductive lines of the die 302 (and the package substrate 304, discussed below) may extend into and out of the plane of the drawing, providing conductive pathways to route electrical signals to and/or from various elements in the die 302.

The conductive vias and/or lines that provide the conductive pathways 315 in the die 302 may be formed using any suitable techniques. Examples of such techniques may include subtractive fabrication techniques, additive or semi-additive fabrication techniques, single Damascene fabrication techniques, dual Damascene fabrication techniques, or any other suitable technique. In some embodiments, layers of oxide material 390 and layers of nitride material 391 may insulate various structures in the conductive pathways 315 from proximate structures, and/or may serve as etch stops during fabrication. In some embodiments, an adhesion layer (not shown) may be disposed between conductive material and proximate insulating material of the die 302 to improve mechanical adhesion between the conductive material and the insulating material.

The gates 106/108, the doped regions 140, and the quantum well stack 146 (as well as the proximate conductive vias/lines) may be referred to as part of the “device layer” of the quantum dot device 100. The conductive lines 393 may be referred to as a Metal 1 or “M1” interconnect layer, and may couple the structures in the device layer to other interconnect structures. The conductive vias 398 and the conductive lines 396 may be referred to as a Metal 2 or “M2” interconnect layer, and may be formed directly on the M1 interconnect layer.

A solder resist material 367 may be disposed around the conductive contacts 365, and, in some embodiments, may extend onto the conductive contacts 365. The solder resist material 367 may be a polyimide or similar material, or may be any appropriate type of packaging solder resist material. In some embodiments, the solder resist material 367 may be a liquid or dry film material including photoimageable polymers. In some embodiments, the solder resist material 367 may be non-photoimageable (and openings therein may be formed using laser drilling or masked etch techniques). The conductive contacts 365 may provide the contacts to couple other components (e.g., a package substrate 304, as discussed below, or another component) to the conductive pathways 315 in the quantum dot device 100, and may be formed of any suitable conductive material (e.g., a superconducting material). For example, solder bonds may be formed on the one or more conductive contacts 365 to mechanically and/or electrically couple the die 302 with another component (e.g., a circuit board), as discussed below. The conductive contacts 365 illustrated in FIG. 62 take the form of bond pads, but other first-level interconnect structures may be used (e.g., posts) to route electrical signals to/from the die 302, as discussed below.

The combination of the conductive pathways and the proximate insulating material (e.g., the insulating material 130, the oxide material 390, and the nitride material 391) in the die 302 may provide an ILD stack of the die 302. As noted above, interconnect structures may be arranged within the quantum dot device 100 to route electrical signals according to a wide variety of designs (in particular, the arrangement is not limited to the particular configuration of interconnect structures depicted in FIG. 62 or any of the other accompanying figures, and may include more or fewer interconnect structures). During operation of the quantum dot device 100, electrical signals (such as power and/or input/output (I/O) signals) may be routed to and/or from the gates 106/108, the magnet line(s) 121, and/or the doped regions 140 (and/or other components) of the quantum dot device 100 through the interconnects provided by conductive vias and/or lines, and through the conductive pathways of the package substrate 304 (discussed below).

Example superconducting materials that may be used for the structures in the conductive pathways 313, 317, 319 (discussed below), and 315, and/or conductive contacts of the die 302 and/or the package substrate 304, may include aluminum, niobium, tin, titanium, osmium, zinc, molybdenum, tantalum, vanadium, or composites of such materials (e.g., niobium titanium, niobium aluminum, or niobium tin). In some embodiments, the conductive contacts 365, 379, and/or 399 may include aluminum, and the first-level interconnects 306 and/or the second-level interconnects 308 may include an indium-based solder.

As noted above, the quantum dot device package 300 of FIG. 63 may include a die 302 (including one or more quantum dot devices 100) and a die 350. As discussed in detail below, the quantum dot device package 300 may include electrical pathways between the die 302 and the die 350 so that the dies 302 and 350 may communicate during operation. In some embodiments, the die 350 may be a non-quantum logic device that may provide support or control functionality for the quantum dot device(s) 100 of the die 302. For example, as discussed further below, in some embodiments, the die 350 may include a switching matrix to control the writing and reading of data from the die 302 (e.g., using any known word line/bit line or other addressing architecture). In some embodiments, the die 350 may control the voltages (e.g., microwave pulses or constant voltages) applied to the gates 106/108 and/or the doped regions 140 of the quantum dot device(s) 100 included in the die 302. In some embodiments, the die 350 may include magnet line control logic to provide microwave pulses to the magnet line(s) 121 of the quantum dot device(s) 100 in the die 302. The die 350 may include any desired control circuitry to support operation of the die 302. By including this control circuitry in a separate die, the manufacture of the die 302 may be simplified and focused on the needs of the quantum computations performed by the quantum dot device(s) 100, and conventional manufacturing and design processes for control logic (e.g., switching array logic) may be used to form the die 350.

Although a singular “die 350” is illustrated in FIG. 63 and discussed herein, the functionality provided by the die 350 may, in some embodiments, be distributed across multiple dies 350 (e.g., multiple dies coupled to the package substrate 304, or otherwise sharing a common support with the die 302). Similarly, one or more dies providing the functionality of the die 350 may support one or more dies providing the functionality of the die 302; for example, the quantum dot device package 300 may include multiple dies having one or more quantum dot devices 100, and a die 350 may communicate with one or more such “quantum dot device dies.”

The die 350 may take any of the forms discussed below with reference to the non-quantum processing device 2028 of FIG. 67 . Mechanisms by which the control logic of the die 350 may control operation of the die 302 may be take the form of an entirely hardware embodiment or an embodiment combining software and hardware aspects. For example, the die 350 may implement an algorithm executed by one or more processing units, e.g. one or more microprocessors. In various embodiments, aspects of the present disclosure may take the form of a computer program product embodied in one or more computer readable medium(s), preferably non-transitory, having computer readable program code embodied (e.g., stored) in or coupled to the die 350. In various embodiments, such a computer program may, for example, be downloaded (updated) to the die 350 (or attendant memory) or be stored upon manufacturing of the die 350. In some embodiments, the die 350 may include at least one processor and at least one memory element, along with any other suitable hardware and/or software to enable its intended functionality of controlling operation of the die 302 as described herein. A processor of the die 350 may execute software or an algorithm to perform the activities discussed herein. A processor of the die 350 may be communicatively coupled to other system elements via one or more interconnects or buses (e.g., through one or more conductive pathways 319). Such a processor may include any combination of hardware, software, or firmware providing programmable logic, including by way of non-limiting example, a microprocessor, a digital signal processor (DSP), a field-programmable gate array (FPGA), a programmable logic array (PLA), an application-specific integrated circuit (ASIC), or a virtual machine processor. The processor of the die 350 may be communicatively coupled to the memory element of the die 350, for example, in a direct-memory access (DMA) configuration. A memory element of the die 350 may include any suitable volatile or nonvolatile memory technology, including double data rate (DDR) random access memory (RAM), synchronous RAM (SRAM), dynamic RAM (DRAM), flash, read-only memory (ROM), optical media, virtual memory regions, magnetic or tape memory, or any other suitable technology. In some embodiments, the memory element and the processor of the “die 350” may themselves be provided by separate physical dies that are in electrical communication. The information being tracked or sent to the die 350 could be provided in any database, register, control list, cache, or storage structure, all of which can be referenced at any suitable timeframe. The die 350 can further include suitable interfaces for receiving, transmitting, and/or otherwise communicating data or information in a network environment (e.g., via the conductive pathways 319).

In some embodiments, the die 350 may be configured to apply appropriate voltages to any one of the gates 106/108 (acting as, e.g., plunger gates, barrier gates, and/or accumulation gates) in order to initialize and manipulate the quantum dots 142, as discussed above. For example, by controlling the voltage applied to a gate 106/108 acting as a plunger gate, the die 350 may modulate the electric field underneath that gate to create an energy valley between the tunnel barriers created by adjacent barrier gates. In another example, by controlling the voltage applied to a gate 106/108 acting as a barrier gate, the die 350 may change the height of the tunnel barrier. When a barrier gate is used to set a tunnel barrier between two plunger gates, the barrier gate may be used to transfer charge carriers between quantum dots 142 that may be formed under these plunger gates. When a barrier gate is used to set a tunnel barrier between a plunger gate and an accumulation gate, the barrier gate may be used to transfer charge carriers in and out of the quantum dot array via the accumulation gate. The term “accumulation gate” may refer to a gate used to form a 2DEG in an area that is between the area where the quantum dots 142 may be formed and a charge carrier reservoir (e.g., the doped regions 140). Changing the voltage applied to the accumulation gate may allow the die 350 to control the number of charge carriers in the area under the accumulation gate. For example, changing the voltage applied to the accumulation gate may reduce the number of charge carriers in the area under the gate so that single charge carriers can be transferred from the reservoir into the quantum well layer 152, and vice versa. In some embodiments, the “outermost” gates 106 in a quantum dot device 100 may serve as accumulation gates. In some embodiments, these outermost gates 106 may have a greater length 168 than “inner” gates 106.

As noted above, the die 350 may provide electrical signals to control spins of charge carriers in quantum dots 142 of the quantum dot device(s) 100 of the die 302 by controlling a magnetic field generated by one or more magnet line(s) 121. In this manner, the die 350 may initialize and manipulate spins of the charge carriers in the quantum dots 142 to implement qubit operations. If the magnetic field for a die 302 is generated by a microwave transmission line, then the die 350 may set/manipulate the spins of the charge carriers by applying appropriate pulse sequences to manipulate spin precession. Alternatively, the magnetic field for a quantum dot device 100 of the die 302 may be generated by a magnet with one or more pulsed gates; the die 350 may apply the pulses to these gates.

In some embodiments, the die 350 may be configured to determine the values of the control signals applied to the elements of the die 302 (e.g. determine the voltages to be applied to the various gates 106/108) to achieve desired quantum operations (communicated to the die 350 through the package substrate 304 via the conductive pathways 319). In other embodiments, the die 350 may be preprogrammed with at least some of the control parameters (e.g. with the values for the voltages to be applied to the various gates 106/108) during the initialization of the die 350.

In the quantum dot device package 300 (FIG. 63 ), first-level interconnects 306 may be disposed between the first face 320 of the die 302 and the second face 326 of a package substrate 304. Having first-level interconnects 306 disposed between the first face 320 of the die 302 and the second face 326 of the package substrate 304 (e.g., using solder bumps as part of flip chip packaging techniques) may enable the quantum dot device package 300 to achieve a smaller footprint and higher die-to-package-substrate connection density than could be achieved using conventional wirebond techniques (in which conductive contacts between the die 302 and the package substrate 304 are constrained to be located on the periphery of the die 302). For example, a die 302 having a square first face 320 with side length N may be able to form only 4N wirebond interconnects to the package substrate 304, versus N² flip chip interconnects (utilizing the entire “full field” surface area of the first face 320). Additionally, in some applications, wirebond interconnects may generate unacceptable amounts of heat that may damage or otherwise interfere with the performance of the quantum dot device 100. Using solder bumps as the first-level interconnects 306 may enable the quantum dot device package 300 to have much lower parasitic inductance relative to using wirebonds to couple the die 302 and the package substrate 304, which may result in an improvement in signal integrity for high speed signals communicated between the die 302 and the package substrate 304. Similarly, first-level interconnects 309 may be disposed between conductive contacts 371 of the die 350 and conductive contacts 379 at the second face 326 of the package substrate 304, as shown, to couple electronic components (not shown) in the die 350 to conductive pathways in the package substrate 304.

The package substrate 304 may include a first face 324 and an opposing second face 326. Conductive contacts 399 may be disposed at the first face 324, and conductive contacts 379 may be disposed at the second face 326. Solder resist material 314 may be disposed around the conductive contacts 379, and solder resist material 312 may be disposed around the conductive contacts 399; the solder resist materials 314 and 312 may take any of the forms discussed above with reference to the solder resist material 367. In some embodiments, the solder resist material 312 and/or the solder resist material 314 may be omitted. Conductive pathways may extend through the insulating material 310 between the first face 324 and the second face 326 of the package substrate 304, electrically coupling various ones of the conductive contacts 399 to various ones of the conductive contacts 379, in any desired manner. The insulating material 310 may be a dielectric material (e.g., an ILD), and may take the form of any of the embodiments of the insulating material 130 disclosed herein, for example. The conductive pathways may include one or more conductive vias 395 and/or one or more conductive lines 397, for example.

For example, the package substrate 304 may include one or more conductive pathways 313 to electrically couple the die 302 to conductive contacts 399 on the first face 324 of the package substrate 304; these conductive pathways 313 may be used to allow the die 302 to electrically communicate with a circuit component to which the quantum dot device package 300 is coupled (e.g., a circuit board or interposer, as discussed below). The package substrate 304 may include one or more conductive pathways 319 to electrically couple the die 350 to conductive contacts 399 on the first face 324 of the package substrate 304; these conductive pathways 319 may be used to allow the die 350 to electrically communicate with a circuit component to which the quantum dot device package 300 is coupled (e.g., a circuit board or interposer, as discussed below).

The package substrate 304 may include one or more conductive pathways 317 to electrically couple the die 302 to the die 350 through the package substrate 304. In particular, the package substrate 304 may include conductive pathways 317 that couple different ones of the conductive contacts 379 on the second face 326 of the package substrate 304 so that, when the die 302 and the die 350 are coupled to these different conductive contacts 379, the die 302 and the die 350 may communicate through the package substrate 304. Although the die 302 and the die 350 are illustrated in FIG. 63 as being disposed on the same second face 326 of the package substrate 304, in some embodiments, the die 302 and the die 350 may be disposed on different faces of the package substrate 304 (e.g., one on the first face 324 and one on the second face 326), and may communicate via one or more conductive pathways 317.

In some embodiments, the conductive pathways 317 may be microwave transmission lines. Microwave transmission lines may be structured for the effective transmission of microwave signals, and may take the form of any microwave transmission lines known in the art. For example, a conductive pathway 317 may be a coplanar waveguide, a stripline, a microstrip line, or an inverted microstrip line. The die 350 may provide microwave pulses along the conductive pathways 317 to the die 302 to provide electron spin resonance (ESR) pulses to the quantum dot device(s) 100 to manipulate the spin states of the quantum dots 142 that form therein. In some embodiments, the die 350 may generate a microwave pulse that is transmitted over a conductive pathway 317 and induces a magnetic field in the magnet line(s) 121 of a quantum dot device 100 and causes a transition between the spin-up and spin-down states of a quantum dot 142. In some embodiments, the die 350 may generate a microwave pulse that is transmitted over a conductive pathway 317 and induces a magnetic field in a gate 106/108 to cause a transition between the spin-up and spin-down states of a quantum dot 142. The die 350 may enable any such embodiments, or any combination of such embodiments.

The die 350 may provide any suitable control signals to the die 302 to enable operation of the quantum dot device(s) 100 included in the die 302. For example, the die 350 may provide voltages (through the conductive pathways 317) to the gates 106/108, and thereby tune the energy profile in the quantum well stack 146.

In some embodiments, the quantum dot device package 300 may be a cored package, one in which the package substrate 304 is built on a carrier material (not shown) that remains in the package substrate 304. In such embodiments, the carrier material may be a dielectric material that is part of the insulating material 310; laser vias or other through-holes may be made through the carrier material to allow conductive pathways 313 and/or 319 to extend between the first face 324 and the second face 326.

In some embodiments, the package substrate 304 may be or may otherwise include a silicon interposer, and the conductive pathways 313 and/or 319 may be through-silicon vias. Silicon may have a desirably low coefficient of thermal expansion compared with other dielectric materials that may be used for the insulating material 310, and thus may limit the degree to which the package substrate 304 expands and contracts during temperature changes relative to such other materials (e.g., polymers having higher coefficients of thermal expansion). A silicon interposer may also help the package substrate 304 achieve a desirably small line width and maintain high connection density to the die 302 and/or the die 350.

Limiting differential expansion and contraction may help preserve the mechanical and electrical integrity of the quantum dot device package 300 as the quantum dot device package 300 is fabricated (and exposed to higher temperatures) and used in a cooled environment (and exposed to lower temperatures). In some embodiments, thermal expansion and contraction in the package substrate 304 may be managed by maintaining an approximately uniform density of the conductive material in the package substrate 304 (so that different portions of the package substrate 304 expand and contract uniformly), using reinforced dielectric materials as the insulating material 310 (e.g., dielectric materials with silicon dioxide fillers), or utilizing stiffer materials as the insulating material 310 (e.g., a prepreg material including glass cloth fibers). In some embodiments, the die 350 may be formed of semiconductor materials or compound semiconductor materials (e.g., group III-group V compounds) to enable higher efficiency amplification and signal generation to minimize the heat generated during operation and reduce the impact on the quantum operations of the die 302. In some embodiments, the metallization in the die 350 may use superconducting materials (e.g., titanium nitride, niobium, niobium nitride, and niobium titanium nitride) to minimize heating.

The conductive contacts 365 of the die 302 may be electrically coupled to the conductive contacts 379 of the package substrate 304 via the first-level interconnects 306, and the conductive contacts 371 of the die 350 may be electrically coupled to the conductive contacts 379 of the package substrate 304 via the first-level interconnects 309. In some embodiments, the first-level interconnects 306/309 may include solder bumps or balls (as illustrated in FIG. 63 ); for example, the first-level interconnects 306/309 may be flip chip (or controlled collapse chip connection, “C4”) bumps disposed initially on the die 302/die 350 or on the package substrate 304. Second-level interconnects 308 (e.g., solder balls or other types of interconnects) may couple the conductive contacts 399 on the first face 324 of the package substrate 304 to another component, such as a circuit board (not shown). Examples of arrangements of electronics packages that may include an embodiment of the quantum dot device package 300 are discussed below with reference to FIG. 65 . The die 302 and/or the die 350 may be brought in contact with the package substrate 304 using a pick-and-place apparatus, for example, and a reflow or thermal compression bonding operation may be used to couple the die 302 and/or the die 350 to the package substrate 304 via the first-level interconnects 306 and/or the first-level interconnects 309, respectively.

The conductive contacts 365, 371, 379, and/or 399 may include multiple layers of material that may be selected to serve different purposes. In some embodiments, the conductive contacts 365, 371, 379, and/or 399 may be formed of aluminum, and may include a layer of gold (e.g., with a thickness of less than 1 micron) between the aluminum and the adjacent interconnect to limit the oxidation of the surface of the contacts and improve the adhesion with adjacent solder. In some embodiments, the conductive contacts 365, 371, 379, and/or 399 may be formed of aluminum, and may include a layer of a barrier metal such as nickel, as well as a layer of gold, wherein the layer of barrier metal is disposed between the aluminum and the layer of gold, and the layer of gold is disposed between the barrier metal and the adjacent interconnect. In such embodiments, the gold may protect the barrier metal surface from oxidation before assembly, and the barrier metal may limit the diffusion of solder from the adjacent interconnects into the aluminum.

In some embodiments, the structures and materials in the quantum dot device 100 may be damaged if the quantum dot device 100 is exposed to the high temperatures that are common in conventional integrated circuit processing (e.g., greater than 100 degrees Celsius, or greater than 200 degrees Celsius). In particular, in embodiments in which the first-level interconnects 306/309 include solder, the solder may be a low temperature solder (e.g., a solder having a melting point below 100 degrees Celsius) so that it can be melted to couple the conductive contacts 365/371 and the conductive contacts 379 without having to expose the die 302 to higher temperatures and risk damaging the quantum dot device 100. Examples of solders that may be suitable include indium-based solders (e.g., solders including indium alloys). When low temperature solders are used, however, these solders may not be fully solid during handling of the quantum dot device package 300 (e.g., at room temperature or temperatures between room temperature and 100 degrees Celsius), and thus the solder of the first-level interconnects 306/309 alone may not reliably mechanically couple the die 302/die 350 and the package substrate 304 (and thus may not reliably electrically couple the die 302/die 350 and the package substrate 304). In some such embodiments, the quantum dot device package 300 may further include a mechanical stabilizer to maintain mechanical coupling between the die 302/die 350 and the package substrate 304, even when solder of the first-level interconnects 306/309 is not solid. Examples of mechanical stabilizers may include an underfill material disposed between the die 302/die 350 and the package substrate 304, a corner glue disposed between the die 302/die 350 and the package substrate 304, an overmold material disposed around the die 302/die 350 on the package substrate 304, and/or a mechanical frame to secure the die 302/die 350 and the package substrate 304.

In some embodiments of the quantum dot device package 300, the die 350 may not be included in the package 300; instead, the die 350 may be electrically coupled to the die 302 through another type of common physical support. For example, the die 350 may be separately packaged from the die 302 (e.g., the die 350 may be mounted to its own package substrate), and the two packages may be coupled together through an interposer, a printed circuit board, a bridge, a package-on-package arrangement, or in any other manner. Examples of device assemblies that may include the die 302 and the die 350 in various arrangements are discussed below with reference to FIG. 65 .

FIGS. 64A-B are top views of a wafer 450 and dies 452 that may be formed from the wafer 450; the dies 452 may be included in any of the quantum dot device packages (e.g., the quantum dot device package 300) disclosed herein. The wafer 450 may include semiconductor material and may include one or more dies 452 having conventional and quantum dot device elements formed on a surface of the wafer 450. Each of the dies 452 may be a repeating unit of a semiconductor product that includes any suitable conventional and/or quantum dot device. After the fabrication of the semiconductor product is complete, the wafer 450 may undergo a singulation process in which each of the dies 452 is separated from the others to provide discrete “chips” of the semiconductor product. A die 452 may include one or more quantum dot devices 100 and/or supporting circuitry to route electrical signals to the quantum dot devices 100 (e.g., interconnects including conductive vias and lines), as well as any other integrated circuit (IC) components. In some embodiments, the wafer 450 or the die 452 may include a memory device (e.g., a static random access memory (SRAM) device), a logic device (e.g., AND, OR, NAND, or NOR gate), or any other suitable circuit element. Multiple ones of these devices may be combined on a single die 452. For example, a memory array formed by multiple memory devices may be formed on a same die 452 as a processing device (e.g., the processing device 2002 of FIG. 67 ) or other logic that is configured to store information in the memory devices or execute instructions stored in the memory array.

FIG. 65 is a cross-sectional view of a device assembly 400 that may include any of the embodiments of the quantum dot device packages 300 disclosed herein. The device assembly 400 includes a number of components disposed on a circuit board 402. The device assembly 400 may include components disposed on a first face 440 of the circuit board 402 and an opposing second face 442 of the circuit board 402; generally, components may be disposed on one or both faces 440 and 442.

In some embodiments, the circuit board 402 may be a printed circuit board (PCB) including multiple metal layers separated from one another by layers of dielectric material and interconnected by electrically conductive vias. Any one or more of the metal layers may be formed in a desired circuit pattern to route electrical signals (optionally in conjunction with other metal layers) between the components coupled to the circuit board 402. In other embodiments, the circuit board 402 may be a package substrate or flexible board. In some embodiments, the die 302 and the die 350 (FIG. 63 ) may be separately packaged and coupled together via the circuit board 402 (e.g., the conductive pathways 317 may run through the circuit board 402).

The device assembly 400 illustrated in FIG. 65 includes a package-on-interposer structure 436 coupled to the first face 440 of the circuit board 402 by coupling components 416. The coupling components 416 may electrically and mechanically couple the package-on-interposer structure 436 to the circuit board 402, and may include solder balls (as shown in FIG. 63 ), male and female portions of a socket, an adhesive, an underfill material, and/or any other suitable electrical and/or mechanical coupling structure.

The package-on-interposer structure 436 may include a package 420 coupled to an interposer 404 by coupling components 418. The coupling components 418 may take any suitable form for the application, such as the forms discussed above with reference to the coupling components 416. For example, the coupling components 418 may be the second-level interconnects 308. Although a single package 420 is shown in FIG. 65 , multiple packages may be coupled to the interposer 404; indeed, additional interposers may be coupled to the interposer 404. The interposer 404 may provide an intervening substrate used to bridge the circuit board 402 and the package 420. The package 420 may be a quantum dot device package 300 or may be a conventional IC package, for example. In some embodiments, the package 420 may take the form of any of the embodiments of the quantum dot device package 300 disclosed herein, and may include a quantum dot device die 302 coupled to a package substrate 304 (e.g., by flip chip connections). Generally, the interposer 404 may spread a connection to a wider pitch or reroute a connection to a different connection. For example, the interposer 404 may couple the package 420 (e.g., a die) to a ball grid array (BGA) of the coupling components 416 for coupling to the circuit board 402. In the embodiment illustrated in FIG. 65 , the package 420 and the circuit board 402 are attached to opposing sides of the interposer 404; in other embodiments, the package 420 and the circuit board 402 may be attached to a same side of the interposer 404. In some embodiments, three or more components may be interconnected by way of the interposer 404. In some embodiments, a quantum dot device package 300 including the die 302 and the die 350 (FIG. 63 ) may be one of the packages disposed on an interposer like the interposer 404. In some embodiments, the die 302 and the die 350 (FIG. 63 ) may be separately packaged and coupled together via the interposer 404 (e.g., the conductive pathways 317 may run through the interposer 404).

The interposer 404 may be formed of an epoxy resin, a fiberglass-reinforced epoxy resin, a ceramic material, or a polymer material such as polyimide. In some embodiments, the interposer 404 may be formed of alternate rigid or flexible materials that may include the same materials described above for use in a semiconductor substrate, such as silicon, germanium, and other group III-group V compounds and group IV materials. The interposer 404 may include metal interconnects 408 and vias 410, including but not limited to through-silicon vias (TSVs) 406. The interposer 404 may further include embedded devices 414, including both passive and active devices. Such devices may include, but are not limited to, capacitors, decoupling capacitors, resistors, inductors, fuses, diodes, transformers, sensors, electrostatic discharge (ESD) devices, and memory devices. More complex devices such as radio frequency (RF) devices, power amplifiers, power management devices, antennas, arrays, sensors, and microelectromechanical systems (MEMS) devices may also be formed on the interposer 404. The package-on-interposer structure 436 may take the form of any of the package-on-interposer structures known in the art.

The device assembly 400 may include a package 424 coupled to the first face 440 of the circuit board 402 by coupling components 422. The coupling components 422 may take the form of any of the embodiments discussed above with reference to the coupling components 416, and the package 424 may take the form of any of the embodiments discussed above with reference to the package 420. The package 424 may be a quantum dot device package 300 (e.g., including the die 302 and the die 350, or just the die 302) or may be a conventional IC package, for example. In some embodiments, the package 424 may take the form of any of the embodiments of the quantum dot device package 300 disclosed herein, and may include a quantum dot device die 302 coupled to a package substrate 304 (e.g., by flip chip connections).

The device assembly 400 illustrated in FIG. 65 includes a package-on-package structure 434 coupled to the second face 442 of the circuit board 402 by coupling components 428. The package-on-package structure 434 may include a package 426 and a package 432 coupled together by coupling components 430 such that the package 426 is disposed between the circuit board 402 and the package 432. The coupling components 428 and 430 may take the form of any of the embodiments of the coupling components 416 discussed above, and the packages 426 and 432 may take the form of any of the embodiments of the package 420 discussed above. Each of the packages 426 and 432 may be a quantum dot device package 300 or may be a conventional IC package, for example. In some embodiments, one or both of the packages 426 and 432 may take the form of any of the embodiments of the quantum dot device package 300 disclosed herein, and may include a die 302 coupled to a package substrate 304 (e.g., by flip chip connections). In some embodiments, a quantum dot device package 300 including the die 302 and the die 350 (FIG. 63 ) may be one of the packages in a package-on-package structure like the package-on-package structure 434. In some embodiments, the die 302 and the die 350 (FIG. 63 ) may be separately packaged and coupled together using a package-on-package structure like the package-on-package structure 434 (e.g., the conductive pathways 317 may run through a package substrate of one or both of the packages of the dies 302 and 350).

A number of techniques are disclosed herein for operating a quantum dot device 100. FIG. 66 is a flow diagram of a particular illustrative method 1020 of operating a quantum dot device, in accordance with various embodiments. Although the operations discussed below with reference to the method 1020 are illustrated in a particular order and depicted once each, these operations may be repeated or performed in a different order (e.g., in parallel), as suitable. Additionally, various operations may be omitted, as suitable. Various operations of the method 1020 may be illustrated with reference to one or more of the embodiments discussed above, but the method 1020 may be used to operate any suitable quantum dot device (including any suitable ones of the embodiments disclosed herein).

At 1022, electrical signals may be provided to one or more first gates disposed above a quantum well stack as part of causing a first quantum well to form in a quantum well layer in the quantum well stack. The quantum well stack may take the form of any of the embodiments disclosed herein (e.g., the quantum well stacks 146 discussed above with reference to FIGS. 50-52 ), and may be included in any of the quantum dot devices 100 disclosed herein. For example, a voltage may be applied to a gate 108-11 as part of causing a first quantum well (for a first quantum dot 142) to form in the quantum well stack 146 below the gate 108-11.

At 1024, electrical signals may be provided to one or more second gates disposed above the quantum well stack as part of causing a second quantum well to form in the quantum well layer. For example, a voltage may be applied to the gate 108-12 as part of causing a second quantum well (for a second quantum dot 142) to form in the quantum well stack 146 below the gate 108-12.

At 1026, electrical signals may be provided to one or more third gates disposed above the quantum well stack as part of (1) causing a third quantum well to form in the quantum well layer or (2) providing a potential barrier between the first quantum well and the second quantum well. For example, a voltage may be applied to the gate 106-12 as part of (1) causing a third quantum well (for a third quantum dot 142) to form in the quantum well stack 146 below the gate 106-12 (e.g., when the gate 106-12 acts as a “plunger” gate) or (2) providing a potential barrier between the first quantum well (under the gate 108-11) and the second quantum well (under the gate 108-12) (e.g., when the gate 106-12 acts as a “barrier” gate).

FIG. 67 is a block diagram of an example quantum computing device 2000 that may include any of the quantum dot devices disclosed herein. A number of components are illustrated in FIG. 67 as included in the quantum computing device 2000, but any one or more of these components may be omitted or duplicated, as suitable for the application. In some embodiments, some or all of the components included in the quantum computing device 2000 may be attached to one or more PCBs (e.g., a motherboard). In some embodiments, various ones of these components may be fabricated onto a single SoC die. Additionally, in various embodiments, the quantum computing device 2000 may not include one or more of the components illustrated in FIG. 67 , but the quantum computing device 2000 may include interface circuitry for coupling to the one or more components. For example, the quantum computing device 2000 may not include a display device 2006, but may include display device interface circuitry (e.g., a connector and driver circuitry) to which a display device 2006 may be coupled. In another set of examples, the quantum computing device 2000 may not include an audio input device 2024 or an audio output device 2008, but may include audio input or output device interface circuitry (e.g., connectors and supporting circuitry) to which an audio input device 2024 or audio output device 2008 may be coupled.

The quantum computing device 2000 may include a processing device 2002 (e.g., one or more processing devices). As used herein, the term “processing device” or “processor” may refer to any device or portion of a device that processes electronic data from registers and/or memory to transform that electronic data into other electronic data that may be stored in registers and/or memory. The processing device 2002 may include a quantum processing device 2026 (e.g., one or more quantum processing devices), and a non-quantum processing device 2028 (e.g., one or more non-quantum processing devices). The quantum processing device 2026 may include one or more of the quantum dot devices 100 disclosed herein, and may perform data processing by performing operations on the quantum dots that may be generated in the quantum dot devices 100, and monitoring the result of those operations. For example, as discussed above, different quantum dots may be allowed to interact, the quantum states of different quantum dots may be set or transformed, and the quantum states of quantum dots may be read (e.g., by another quantum dot). The quantum processing device 2026 may be a universal quantum processor, or specialized quantum processor configured to run one or more particular quantum algorithms. In some embodiments, the quantum processing device 2026 may execute algorithms that are particularly suitable for quantum computers, such as cryptographic algorithms that utilize prime factorization, encryption/decryption, algorithms to optimize chemical reactions, algorithms to model protein folding, etc. The quantum processing device 2026 may also include support circuitry to support the processing capability of the quantum processing device 2026, such as input/output channels, multiplexers, signal mixers, quantum amplifiers, and analog-to-digital converters. For example, the quantum processing device 2026 may include circuitry (e.g., a current source) to provide current pulses to one or more magnet lines 121 included in the quantum dot device 100.

As noted above, the processing device 2002 may include a non-quantum processing device 2028. In some embodiments, the non-quantum processing device 2028 may provide peripheral logic to support the operation of the quantum processing device 2026. For example, the non-quantum processing device 2028 may control the performance of a read operation, control the performance of a write operation, control the clearing of quantum bits, etc. The non-quantum processing device 2028 may also perform conventional computing functions to supplement the computing functions provided by the quantum processing device 2026. For example, the non-quantum processing device 2028 may interface with one or more of the other components of the quantum computing device 2000 (e.g., the communication chip 2012 discussed below, the display device 2006 discussed below, etc.) in a conventional manner, and may serve as an interface between the quantum processing device 2026 and conventional components. The non-quantum processing device 2028 may include one or more DSPs, ASICs, central processing units (CPUs), graphics processing units (GPUs), cryptoprocessors (specialized processors that execute cryptographic algorithms within hardware), server processors, or any other suitable processing devices.

The quantum computing device 2000 may include a memory 2004, which may itself include one or more memory devices such as volatile memory (e.g., dynamic random access memory (DRAM)), nonvolatile memory (e.g., ROM), flash memory, solid state memory, and/or a hard drive. In some embodiments, the states of qubits in the quantum processing device 2026 may be read and stored in the memory 2004. In some embodiments, the memory 2004 may include memory that shares a die with the non-quantum processing device 2028. This memory may be used as cache memory and may include embedded dynamic random access memory (eDRAM) or spin transfer torque magnetic random access memory (STT-MRAM).

The quantum computing device 2000 may include a cooling apparatus 2030. The cooling apparatus 2030 may maintain the quantum processing device 2026 at a predetermined low temperature during operation to reduce the effects of scattering in the quantum processing device 2026. This predetermined low temperature may vary depending on the setting; in some embodiments, the temperature may be 5 Kelvin or less. In some embodiments, the non-quantum processing device 2028 (and various other components of the quantum computing device 2000) may not be cooled by the cooling apparatus 2030, and may instead operate at room temperature. The cooling apparatus 2030 may be, for example, a dilution refrigerator, a helium-3 refrigerator, or a liquid helium refrigerator.

In some embodiments, the quantum computing device 2000 may include a communication chip 2012 (e.g., one or more communication chips). For example, the communication chip 2012 may be configured for managing wireless communications for the transfer of data to and from the quantum computing device 2000. The term “wireless” and its derivatives may be used to describe circuits, devices, systems, methods, techniques, communications channels, etc., that may communicate data through the use of modulated electromagnetic radiation through a nonsolid medium. The term does not imply that the associated devices do not contain any wires, although in some embodiments they might not.

The communication chip 2012 may implement any of a number of wireless standards or protocols, including but not limited to Institute for Electrical and Electronic Engineers (IEEE) standards including Wi-Fi (IEEE 802.11 family), IEEE 802.16 standards (e.g., IEEE 802.16-2005 Amendment), Long-Term Evolution (LTE) project along with any amendments, updates, and/or revisions (e.g., advanced LTE project, ultramobile broadband (UMB) project (also referred to as “3GPP2”), etc.). IEEE 802.16 compatible Broadband Wireless Access (BWA) networks are generally referred to as WiMAX networks, an acronym that stands for Worldwide Interoperability for Microwave Access, which is a certification mark for products that pass conformity and interoperability tests for the IEEE 802.16 standards. The communication chip 2012 may operate in accordance with a Global System for Mobile Communication (GSM), General Packet Radio Service (GPRS), Universal Mobile Telecommunications System (UMTS), High Speed Packet Access (HSPA), Evolved HSPA (E-HSPA), or LTE network. The communication chip 2012 may operate in accordance with Enhanced Data for GSM Evolution (EDGE), GSM EDGE Radio Access Network (GERAN), Universal Terrestrial Radio Access Network (UTRAN), or Evolved UTRAN (E-UTRAN). The communication chip 2012 may operate in accordance with Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Digital Enhanced Cordless Telecommunications (DECT), Evolution-Data Optimized (EV-DO), and derivatives thereof, as well as any other wireless protocols that are designated as 3G, 4G, 5G, and beyond. The communication chip 2012 may operate in accordance with other wireless protocols in other embodiments. The quantum computing device 2000 may include an antenna 2022 to facilitate wireless communications and/or to receive other wireless communications (such as AM or FM radio transmissions).

In some embodiments, the communication chip 2012 may manage wired communications, such as electrical, optical, or any other suitable communication protocols (e.g., the Ethernet). As noted above, the communication chip 2012 may include multiple communication chips. For instance, a first communication chip 2012 may be dedicated to shorter-range wireless communications such as Wi-Fi or Bluetooth, and a second communication chip 2012 may be dedicated to longer-range wireless communications such as global positioning system (GPS), EDGE, GPRS, CDMA, WiMAX, LTE, EV-DO, or others. In some embodiments, a first communication chip 2012 may be dedicated to wireless communications, and a second communication chip 2012 may be dedicated to wired communications.

The quantum computing device 2000 may include battery/power circuitry 2014. The battery/power circuitry 2014 may include one or more energy storage devices (e.g., batteries or capacitors) and/or circuitry for coupling components of the quantum computing device 2000 to an energy source separate from the quantum computing device 2000 (e.g., AC line power).

The quantum computing device 2000 may include a display device 2006 (or corresponding interface circuitry, as discussed above). The display device 2006 may include any visual indicators, such as a heads-up display, a computer monitor, a projector, a touchscreen display, a liquid crystal display (LCD), a light-emitting diode display, or a flat panel display, for example.

The quantum computing device 2000 may include an audio output device 2008 (or corresponding interface circuitry, as discussed above). The audio output device 2008 may include any device that generates an audible indicator, such as speakers, headsets, or earbuds, for example.

The quantum computing device 2000 may include an audio input device 2024 (or corresponding interface circuitry, as discussed above). The audio input device 2024 may include any device that generates a signal representative of a sound, such as microphones, microphone arrays, or digital instruments (e.g., instruments having a musical instrument digital interface (MIDI) output).

The quantum computing device 2000 may include a GPS device 2018 (or corresponding interface circuitry, as discussed above). The GPS device 2018 may be in communication with a satellite-based system and may receive a location of the quantum computing device 2000, as known in the art.

The quantum computing device 2000 may include an other output device 2010 (or corresponding interface circuitry, as discussed above). Examples of the other output device 2010 may include an audio codec, a video codec, a printer, a wired or wireless transmitter for providing information to other devices, or an additional storage device.

The quantum computing device 2000 may include an other input device 2020 (or corresponding interface circuitry, as discussed above). Examples of the other input device 2020 may include an accelerometer, a gyroscope, a compass, an image capture device, a keyboard, a cursor control device such as a mouse, a stylus, a touchpad, a bar code reader, a Quick Response (QR) code reader, any sensor, or a radio frequency identification (RFID) reader.

The quantum computing device 2000, or a subset of its components, may have any appropriate form factor, such as a hand-held or mobile computing device (e.g., a cell phone, a smart phone, a mobile internet device, a music player, a tablet computer, a laptop computer, a netbook computer, an ultrabook computer, a personal digital assistant (PDA), an ultramobile personal computer, etc.), a desktop computing device, a server or other networked computing component, a printer, a scanner, a monitor, a set-top box, an entertainment control unit, a vehicle control unit, a digital camera, a digital video recorder, or a wearable computing device.

The following paragraphs provide various examples of the embodiments disclosed herein.

Example 1 is a quantum dot device, including: a quantum well stack; an insulating material above the quantum well stack, wherein the insulating material includes a trench; and a gate on the insulating material and extending into the trench, wherein the gate includes a first gate metal in the trench and a second gate metal above the first gate metal.

Example 2 includes the subject matter of Example 1, and further specifies that the trench is a first trench, the gate is a first gate, the insulating material further includes a second trench, and the quantum dot device further comprises: a second gate on the insulating material and extending into the second trench, wherein the second gate includes a third gate metal in the second trench and a fourth gate metal above the third gate metal.

Example 3 includes the subject matter of Example 2, and further specifies that the first and second trenches are parallel.

Example 4 includes the subject matter of any of Examples 2-3, and further specifies that the first and second trenches are spaced apart by a distance between 50 nanometers and 250 nanometers.

Example 5 includes the subject matter of any of Examples 1-4, and further specifies that the trench has a tapered profile that is narrowest proximate to the quantum well stack.

Example 6 includes the subject matter of any of Examples 1-5, and further specifies that the trench extends down to the quantum well stack.

Example 7 includes the subject matter of any of Examples 1-6, and further specifies that the trench has a width between 5 nanometers and 30 nanometers.

Example 8 includes the subject matter of any of Examples 1-7, and further specifies that the gate has a thickness above the insulating material between 25 nanometers and 75 nanometers.

Example 9 includes the subject matter of any of Examples 1-8, and further specifies that the quantum well stack includes silicon or germanium.

Example 10 includes the subject matter of Example 9, and further includes: a semiconductor substrate; wherein the quantum well stack includes a quantum well layer and a barrier layer, and the barrier layer is between the semiconductor substrate and the quantum well layer.

Example 11 includes the subject matter of Example 10, and further specifies that the barrier layer includes silicon germanium.

Example 12 includes the subject matter of any of Examples 1-11, and further specifies that a gate dielectric is at a bottom of the trench.

Example 13 includes the subject matter of any of Examples 1-12, and further specifies that a seam is present between the first gate metal and the second gate metal.

Example 14 includes the subject matter of any of Examples 1-13, and further includes: a magnet line.

Example 15 includes the subject matter of any of Examples 13-14, and further specifies that the magnet line includes a portion that is oriented parallel to a longitudinal axis of the trench, or the magnet line includes a portion that is oriented perpendicular to a longitudinal axis of the trench.

Example 16 includes the subject matter of any of Examples 1-15, and further specifies that the quantum well stack includes a silicon/silicon germanium material stack.

Example 17 includes the subject matter of any of Examples 1-15, and further specifies that the quantum well stack includes a silicon/silicon oxide material stack.

Example 18 includes the subject matter of any of Examples 1-17, and further specifies that the gate has a length, along the trench, between 20 nanometers and 40 nanometers.

Example 19 includes the subject matter of any of Examples 1-18, and further specifies that the gate is a first gate, and the quantum dot device further comprises: a second gate on the insulating material and extending into the trench, wherein the second gate is electrically insulated from the first gate.

Example 20 includes the subject matter of Example 19, and further includes: at least one spacer between the first gate and the second gate.

Example 21 includes the subject matter of Example 20, and further specifies that the at least one spacer has a thickness between 1 nanometer and 10 nanometers.

Example 22 includes the subject matter of any of Examples 20-21, and further specifies that the at least one spacer between the first gate and the second gate includes a stack of two spacers.

Example 23 includes the subject matter of Example 22, and further specifies that a bottom spacer in the stack of two spacers is in the trench and a top spacer in the stack of two spacers is above the trench.

Example 24 includes the subject matter of any of Examples 19-23, and further specifies that the second gate includes a third gate metal in the trench and a fourth gate metal above the third gate metal.

Example 25 includes the subject matter of any of Examples 19-23, and further specifies that the second gate includes a third gate metal in the trench and extending above the trench.

Example 26 includes the subject matter of any of Examples 19-25, and further specifies that the second gate includes a gate dielectric.

Example 27 includes the subject matter of Example 26, and further specifies that the gate dielectric is at a bottom of the trench.

Example 28 includes the subject matter of Example 27, and further specifies that the gate dielectric has a U-shaped cross-section.

Example 29 includes the subject matter of any of Examples 1-28, and further specifies that the trench has a depth between 40 nanometers and 300 nanometers.

Example 30 includes the subject matter of any of Examples 1-29, and further specifies that the first gate metal and the second gate metal have a same material composition.

Example 31 includes the subject matter of any of Examples 1-30, and further specifies that the first gate metal and the second gate metal have different microstructures.

Example 32 includes the subject matter of any of Examples 1-31, and further specifies that the first gate metal includes columnar grains.

Example 33 includes the subject matter of any of Examples 1-32, and further specifies that the first gate metal includes titanium and nitrogen.

Example 34 includes the subject matter of Example 33, and further specifies that the second gate metal includes titanium and nitrogen.

Example 35 is a method of operating a quantum dot device, including: providing electrical signals to one or more first gates at least partially in a first trench in an insulating material to cause a first quantum dot to form in a quantum well stack below the first trench, wherein at least one first gate includes a first layer of gate metal in the first trench and a second layer of gate metal above the first layer of gate metal; providing electrical signals to one or more second gates at least partially in a second trench in the insulating material to cause a second quantum dot to form in the quantum well stack; and sensing a quantum state of the first quantum dot with the second quantum dot.

Example 36 includes the subject matter of Example 35, and further specifies that the first and second trenches are spaced apart by a minimum distance between 50 nanometers and 250 nanometers.

Example 37 includes the subject matter of any of Examples 35-36, and further specifies that the one or more first gates includes three or more first gates separated by spacer material in the first trench.

Example 38 includes the subject matter of any of Examples 35-37, and further specifies that sensing the quantum state of the first quantum dot with the second quantum dot comprises sensing a spin state of the first quantum dot with the second quantum dot.

Example 39 includes the subject matter of any of Examples 35-38, and further specifies that one of the first gates and another of the first gates are spaced apart by spacer material.

Example 40 includes the subject matter of Example 39, and further specifies that the space material includes a stack of two spacers.

Example 41 includes the subject matter of Example 40, and further specifies that a bottom spacer in the stack of two spacers is in the first trench and a top spacer in the stack of two spacers is above the first trench.

Example 42 includes the subject matter of any of Examples 39-41, and further specifies that the another first gate includes a first layer of gate metal in the first trench and a second layer of gate metal above the first layer of gate metal.

Example 43 includes the subject matter of any of Examples 39-41, and further specifies that the another first gate includes a layer of gate metal that is in the first trench and extends above the first trench.

Example 44 includes the subject matter of any of Examples 39-43, and further specifies that the another first gate includes a gate dielectric.

Example 45 includes the subject matter of Example 44, and further specifies that the gate dielectric is at a bottom of the first trench.

Example 46 includes the subject matter of Example 45, and further specifies that the gate dielectric has a U-shaped cross-section.

Example 47 includes the subject matter of any of Examples 35-46, and further specifies that the first layer of gate metal and the second layer of gate metal have a same material composition.

Example 48 includes the subject matter of any of Examples 35-47, and further specifies that the first layer of gate metal and the second layer of gate metal have different microstructures.

Example 49 includes the subject matter of any of Examples 35-48, and further specifies that the first layer of gate metal includes columnar grains.

Example 50 includes the subject matter of any of Examples 35-48, and further specifies that the first layer of gate metal includes titanium and nitrogen.

Example 51 includes the subject matter of Example 50, and further specifies that the second layer of gate metal includes titanium and nitrogen.

Example 52 includes the subject matter of any of Examples 35-51, and further includes: providing electrical signals to the one or more first gates to cause a third quantum dot to form in the quantum well stack; and prior to sensing the quantum state of the first quantum dot with the second quantum dot, allowing the first and third quantum dots to interact.

Example 53 includes the subject matter of Example 52, and further specifies that allowing the first and third quantum dots to interact comprises providing electrical signals to the one or more first gates to control interaction between the first and third quantum dots.

Example 54 includes the subject matter of any of Examples 35-53, and further specifies that the first and second trenches are parallel.

Example 55 is a method of manufacturing a quantum dot device, including: forming a quantum well stack; forming an insulating material above the quantum well stack, wherein the insulating material includes a trench; and forming a gate, wherein the gate includes a first gate metal in the trench and a second gate metal above the first gate metal.

Example 56 includes the subject matter of Example 55, and further specifies that forming the insulating material above the quantum well stack includes: depositing the insulating material above the quantum well stack; and removing at least some of the insulating material to form the trench.

Example 57 includes the subject matter of Example 55, and further specifies that forming the insulating material above the quantum well stack includes: depositing the insulating material over the first gate metal; and polishing back the insulating material.

Example 58 includes the subject matter of Example 55, and further specifies that the first gate metal is formed before the insulating material is formed.

Example 59 includes the subject matter of Example 55, and further specifies that the insulating material is formed before the first gate metal is formed.

Example 60 includes the subject matter of any of Examples 55-59, and further specifies that forming the quantum well stack includes growing material of the quantum well stack by epitaxy.

Example 61 includes the subject matter of any of Examples 55-60, and further includes: providing an interlayer dielectric on the gate; and forming a conductive via through the interlayer dielectric to make conductive contact with the gate.

Example 62 is a quantum computing device, including: a quantum processing device, wherein the quantum processing device includes an insulating material having a trench that extends toward a quantum well layer, and a plurality of gates, wherein a gate of the plurality of gates includes a first layer of gate metal and a second layer of gate metal, wherein the first layer of gate metal is between the second layer of gate metal and the quantum well layer, the first layer of gate metal is in the trench, and the first layer of gate metal has a different microstructure than the second layer of gate metal; a non-quantum processing device, coupled to the quantum processing device, to control voltages applied to a plurality of gates of the quantum processing device; and a memory device to store data generated by quantum dots formed in the quantum well layer during operation of the quantum processing device.

Example 63 includes the subject matter of Example 62, and further includes: a cooling apparatus to maintain a temperature of the quantum processing device below 5 Kelvin.

Example 64 includes the subject matter of Example 63, and further specifies that the cooling apparatus includes a dilution refrigerator.

Example 65 includes the subject matter of Example 63, and further specifies that the cooling apparatus includes a liquid helium refrigerator.

Example 66 includes the subject matter of any of Examples 62-65, and further specifies that the memory device is to store instructions for a quantum computing algorithm to be executed by the quantum processing device.

Example 67 includes the subject matter of any of Examples 62-66, and further specifies that the gate is a first gate, the plurality of gates includes a second gate, and the first gate and the second gate are spaced apart by spacer material.

Example 68 includes the subject matter of Example 67, and further specifies that the space material includes a stack of two spacers.

Example 69 includes the subject matter of Example 68, and further specifies that a bottom spacer in the stack of two spacers is in the trench and a top spacer in the stack of two spacers is above the trench.

Example 70 includes the subject matter of any of Examples 67-69, and further specifies that the second gate includes a first layer of gate metal in the trench and a second layer of gate metal above the first layer of gate metal of the second gate.

Example 71 includes the subject matter of any of Examples 67-69, and further specifies that the second gate includes a layer of gate metal that is in the trench and extends above the trench.

Example 72 includes the subject matter of any of Examples 67-71, and further specifies that the second gate includes a gate dielectric.

Example 73 includes the subject matter of Example 72, and further specifies that the gate dielectric is at a bottom of the trench.

Example 74 includes the subject matter of Example 73, and further specifies that the gate dielectric has a U-shaped cross-section.

Example 75 includes the subject matter of any of Examples 62-74, and further specifies that the first layer of gate metal and the second layer of gate metal have a same material composition.

Example 76 includes the subject matter of any of Examples 62-75, and further specifies that the first layer of gate metal and the second layer of gate metal have different microstructures.

Example 77 includes the subject matter of any of Examples 62-76, and further specifies that the first layer of gate metal includes columnar grains.

Example 78 includes the subject matter of any of Examples 62-77, and further specifies that the first layer of gate metal includes titanium and nitrogen.

Example 79 includes the subject matter of Example 78, and further specifies that the second layer of gate metal includes titanium and nitrogen.

Example 80 includes the subject matter of any of Examples 62-79, and further specifies that a seam is present between the first layer of gate metal and the second layer of gate metal.

Example 81 is a method of manufacturing a quantum dot device, including any of the methods of manufacture disclosed herein. 

The invention claimed is:
 1. A quantum dot device, comprising: a quantum well stack; an insulating material above the quantum well stack, wherein the insulating material includes a trench; and a gate, wherein the gate includes a first gate metal in the trench and a second gate metal above the first gate metal, wherein at least one of: the first gate metal and the second gate metal have different material compositions, the first gate metal and the second gate metal have different microstructures, or a seam is present between the first gate metal and the second gate metal.
 2. The quantum dot device of claim 1, wherein the trench is a first trench, the gate is a first gate, the insulating material further includes a second trench, and the quantum dot device further comprises: a second gate on the insulating material and extending into the second trench, wherein the second gate includes a third gate metal in the second trench and a fourth gate metal above the third gate metal.
 3. The quantum dot device of claim 1, wherein the trench has a tapered profile that is narrowest proximate to the quantum well stack.
 4. The quantum dot device of claim 1, wherein the trench extends down to the quantum well stack.
 5. The quantum dot device of claim 1, wherein the gate is a first gate, and the quantum dot device further comprises: a second gate on the insulating material and extending into the trench, wherein the second gate is electrically insulated from the first gate.
 6. The quantum dot device of claim 5, further comprising: at least one spacer between the first gate and the second gate.
 7. The quantum dot device of claim 6, wherein the at least one spacer between the first gate and the second gate includes a stack of two spacers.
 8. The quantum dot device of claim 7, wherein a bottom spacer in the stack of two spacers is in the trench and a top spacer in the stack of two spacers is above the trench.
 9. The quantum dot device of claim 5, wherein the second gate includes a third gate metal in the trench and a fourth gate metal above the third gate metal.
 10. The quantum dot device of claim 5, wherein the second gate includes a third gate metal in the trench and extending above the trench.
 11. The quantum dot device of claim 1, wherein the first gate metal includes columnar grains.
 12. A method of manufacturing a quantum dot device, the method comprising: forming a quantum well stack; forming an insulating material above the quantum well stack, wherein the insulating material includes a trench; and forming a gate, wherein the gate includes a first gate metal in the trench and a second gate metal above the first gate metal, wherein at least one of: the first gate metal and the second gate metal have different material compositions, the first gate metal and the second gate metal have different microstructures, or a seam is present between the first gate metal and the second gate metal.
 13. The method of claim 12, wherein forming the insulating material above the quantum well stack includes: depositing the insulating material above the quantum well stack; and removing at least some of the insulating material to form the trench.
 14. The method of claim 12, wherein forming the insulating material above the quantum well stack includes: depositing the insulating material over the first gate metal; and polishing back the insulating material.
 15. A quantum computing device, comprising: a quantum processing device, wherein the quantum processing device includes an insulating material having a trench that extends toward a quantum well layer, and a plurality of gates, wherein a gate of the plurality of gates includes a first layer of gate metal and a second layer of gate metal, wherein the first layer of gate metal is between the second layer of gate metal and the quantum well layer, the first layer of gate metal is in the trench, and the first layer of gate metal has a different microstructure than the second layer of gate metal; a non-quantum processing device, coupled to the quantum processing device, to control voltages applied to the plurality of gates of the quantum processing device; and a memory device to store data generated by quantum dots formed in the quantum well layer during operation of the quantum processing device.
 16. The quantum computing device of claim 15, wherein the memory device is to store instructions for a quantum computing algorithm to be executed by the quantum processing device.
 17. The quantum computing device of claim 15, wherein the first layer of gate metal and the second layer of gate metal have different material compositions.
 18. The quantum computing device of claim 15, wherein the first layer of gate metal and the second layer of gate metal have a same material composition.
 19. The quantum computing device of claim 15, wherein the quantum processing device includes a seam between the first layer of gate metal and the second layer of gate metal. 